diff --git a/src/wp-includes/class-wp-customize-setting.php b/src/wp-includes/class-wp-customize-setting.php
index 6630157549..01b84c8e8b 100644
--- a/src/wp-includes/class-wp-customize-setting.php
+++ b/src/wp-includes/class-wp-customize-setting.php
@@ -81,6 +81,25 @@ class WP_Customize_Setting {
 	 */
 	protected $id_data = array();
 
+	/**
+	 * Cache of multidimensional values to improve performance.
+	 *
+	 * @since 4.4.0
+	 * @access protected
+	 * @var array
+	 * @static
+	 */
+	protected static $aggregated_multidimensionals = array();
+
+	/**
+	 * Whether the multidimensional setting is aggregated.
+	 *
+	 * @since 4.4.0
+	 * @access protected
+	 * @var bool
+	 */
+	protected $is_multidimensional_aggregated = false;
+
 	/**
 	 * Constructor.
 	 *
@@ -96,27 +115,80 @@ class WP_Customize_Setting {
 	public function __construct( $manager, $id, $args = array() ) {
 		$keys = array_keys( get_object_vars( $this ) );
 		foreach ( $keys as $key ) {
-			if ( isset( $args[ $key ] ) )
+			if ( isset( $args[ $key ] ) ) {
 				$this->$key = $args[ $key ];
+			}
 		}
 
 		$this->manager = $manager;
 		$this->id = $id;
 
 		// Parse the ID for array keys.
-		$this->id_data[ 'keys' ] = preg_split( '/\[/', str_replace( ']', '', $this->id ) );
-		$this->id_data[ 'base' ] = array_shift( $this->id_data[ 'keys' ] );
+		$this->id_data['keys'] = preg_split( '/\[/', str_replace( ']', '', $this->id ) );
+		$this->id_data['base'] = array_shift( $this->id_data['keys'] );
 
 		// Rebuild the ID.
 		$this->id = $this->id_data[ 'base' ];
-		if ( ! empty( $this->id_data[ 'keys' ] ) )
-			$this->id .= '[' . implode( '][', $this->id_data[ 'keys' ] ) . ']';
+		if ( ! empty( $this->id_data[ 'keys' ] ) ) {
+			$this->id .= '[' . implode( '][', $this->id_data['keys'] ) . ']';
+		}
 
-		if ( $this->sanitize_callback )
+		if ( $this->sanitize_callback ) {
 			add_filter( "customize_sanitize_{$this->id}", $this->sanitize_callback, 10, 2 );
-
-		if ( $this->sanitize_js_callback )
+		}
+		if ( $this->sanitize_js_callback ) {
 			add_filter( "customize_sanitize_js_{$this->id}", $this->sanitize_js_callback, 10, 2 );
+		}
+
+		if ( 'option' === $this->type || 'theme_mod' === $this->type ) {
+			// Other setting types can opt-in to aggregate multidimensional explicitly.
+			$this->aggregate_multidimensional();
+		}
+	}
+
+	/**
+	 * Get parsed ID data for multidimensional setting.
+	 *
+	 * @since 4.4.0
+	 * @access public
+	 *
+	 * @return array {
+	 *     ID data for multidimensional setting.
+	 *
+	 *     @type string $base ID base
+	 *     @type array  $keys Keys for multidimensional array.
+	 * }
+	 */
+	final public function id_data() {
+		return $this->id_data;
+	}
+
+	/**
+	 * Set up the setting for aggregated multidimensional values.
+	 *
+	 * When a multidimensional setting gets aggregated, all of its preview and update
+	 * calls get combined into one call, greatly improving performance.
+	 *
+	 * @since 4.4.0
+	 * @access protected
+	 */
+	protected function aggregate_multidimensional() {
+		if ( empty( $this->id_data['keys'] ) ) {
+			return;
+		}
+
+		$id_base = $this->id_data['base'];
+		if ( ! isset( self::$aggregated_multidimensionals[ $this->type ] ) ) {
+			self::$aggregated_multidimensionals[ $this->type ] = array();
+		}
+		if ( ! isset( self::$aggregated_multidimensionals[ $this->type ][ $id_base ] ) ) {
+			self::$aggregated_multidimensionals[ $this->type ][ $id_base ] = array(
+				'previewed_instances'       => array(), // Calling preview() will add the $setting to the array.
+				'preview_applied_instances' => array(), // Flags for which settings have had their values applied.
+				'root_value'                => $this->get_root_value( array() ), // Root value for initial state, manipulated by preview and update calls.
+			);
+		}
+		$this->is_multidimensional_aggregated = true;
 	}
 
 	/**
@@ -153,29 +225,76 @@ class WP_Customize_Setting {
 	protected $_original_value;
 
 	/**
-	 * Set up filters for the setting so that the preview request
-	 * will render the drafted changes.
+	 * Add filters to supply the setting's value when accessed.
+	 *
+	 * If the setting already has a pre-existing value and there is no incoming
+	 * post value for the setting, then this method will short-circuit since
+	 * there is no change to preview.
 	 *
 	 * @since 3.4.0
+	 * @since 4.4.0 Added boolean return value.
+	 * @access public
+	 *
+	 * @return bool False when preview short-circuits due no change needing to be previewed.
 	 */
 	public function preview() {
-		if ( ! isset( $this->_original_value ) ) {
-			$this->_original_value = $this->value();
-		}
 		if ( ! isset( $this->_previewed_blog_id ) ) {
 			$this->_previewed_blog_id = get_current_blog_id();
 		}
+		$id_base = $this->id_data['base'];
+		$is_multidimensional = ! empty( $this->id_data['keys'] );
+		$multidimensional_filter = array( $this, '_multidimensional_preview_filter' );
 
-		switch( $this->type ) {
+		/*
+		 * Check if the setting has a pre-existing value (an isset check),
+		 * and if doesn't have any incoming post value. If both checks are true,
+		 * then the preview short-circuits because there is nothing that needs
+		 * to be previewed.
+		 */
+		$undefined = new stdClass();
+		$needs_preview = ( $undefined !== $this->post_value( $undefined ) );
+		$value = null;
+
+		// Since no post value was defined, check if we have an initial value set.
+		if ( ! $needs_preview ) {
+			if ( $this->is_multidimensional_aggregated ) {
+				$root = self::$aggregated_multidimensionals[ $this->type ][ $id_base ]['root_value'];
+				$value = $this->multidimensional_get( $root, $this->id_data['keys'], $undefined );
+			} else {
+				$default = $this->default;
+				$this->default = $undefined; // Temporarily set default to undefined so we can detect if existing value is set.
+				$value = $this->value();
+				$this->default = $default;
+			}
+			$needs_preview = ( $undefined === $value ); // Because the default needs to be supplied.
+		}
+
+		if ( ! $needs_preview ) {
+			return false;
+		}
+
+		switch ( $this->type ) {
 			case 'theme_mod' :
-				add_filter( 'theme_mod_' . $this->id_data[ 'base' ], array( $this, '_preview_filter' ) );
+				if ( ! $is_multidimensional ) {
+					add_filter( "theme_mod_{$id_base}", array( $this, '_preview_filter' ) );
+				} else {
+					if ( empty( self::$aggregated_multidimensionals[ $this->type ][ $id_base ]['previewed_instances'] ) ) {
+						// Only add this filter once for this ID base.
+						add_filter( "theme_mod_{$id_base}", $multidimensional_filter );
+					}
+					self::$aggregated_multidimensionals[ $this->type ][ $id_base ]['previewed_instances'][ $this->id ] = $this;
+				}
 				break;
 			case 'option' :
-				if ( empty( $this->id_data[ 'keys' ] ) )
-					add_filter( 'pre_option_' . $this->id_data[ 'base' ], array( $this, '_preview_filter' ) );
-				else {
-					add_filter( 'option_' . $this->id_data[ 'base' ], array( $this, '_preview_filter' ) );
-					add_filter( 'default_option_' . $this->id_data[ 'base' ], array( $this, '_preview_filter' ) );
+				if ( ! $is_multidimensional ) {
+					add_filter( "pre_option_{$id_base}", array( $this, '_preview_filter' ) );
+				} else {
+					if ( empty( self::$aggregated_multidimensionals[ $this->type ][ $id_base ]['previewed_instances'] ) ) {
+						// Only add these filters once for this ID base.
+						add_filter( "option_{$id_base}", $multidimensional_filter );
+						add_filter( "default_option_{$id_base}", $multidimensional_filter );
+					}
+					self::$aggregated_multidimensionals[ $this->type ][ $id_base ]['previewed_instances'][ $this->id ] = $this;
 				}
 				break;
 			default :
@@ -204,17 +323,17 @@ class WP_Customize_Setting {
 				 */
 				do_action( "customize_preview_{$this->type}", $this );
 		}
+		return true;
 	}
 
 	/**
-	 * Callback function to filter the theme mods and options.
+	 * Callback function to filter non-multidimensional theme mods and options.
 	 *
 	 * If switch_to_blog() was called after the preview() method, and the current
 	 * blog is now not the same blog, then this method does a no-op and returns
 	 * the original value.
 	 *
 	 * @since 3.4.0
-	 * @uses WP_Customize_Setting::multidimensional_replace()
 	 *
 	 * @param mixed $original Old value.
 	 * @return mixed New or old value.
@@ -224,15 +343,63 @@ class WP_Customize_Setting {
 			return $original;
 		}
 
-		$undefined = new stdClass(); // symbol hack
+		$undefined = new stdClass(); // Symbol hack.
 		$post_value = $this->post_value( $undefined );
-		if ( $undefined === $post_value ) {
-			$value = $this->_original_value;
-		} else {
+		if ( $undefined !== $post_value ) {
 			$value = $post_value;
+		} else {
+			/*
+			 * Note that we don't use $original here because preview() will
+			 * not add the filter in the first place if it has an initial value
+			 * and there is no post value.
+			 */
+			$value = $this->default;
+		}
+		return $value;
+	}
+
+	/**
+	 * Callback function to filter multidimensional theme mods and options.
+	 *
+	 * For all multidimensional settings of a given type, the preview filter for
+	 * the first setting previewed will be used to apply the values for the others.
+	 *
+	 * @since 4.4.0
+	 * @access public
+	 *
+	 * @see WP_Customize_Setting::$aggregated_multidimensionals
+	 * @param mixed $original Original root value.
+	 * @return mixed New or old value.
+	 */
+	public function _multidimensional_preview_filter( $original ) {
+		if ( ! $this->is_current_blog_previewed() ) {
+			return $original;
 		}
 
-		return $this->multidimensional_replace( $original, $this->id_data['keys'], $value );
+		$id_base = $this->id_data['base'];
+
+		// If no settings have been previewed yet (which should not be the case, since $this is), just pass through the original value.
+		if ( empty( self::$aggregated_multidimensionals[ $this->type ][ $id_base ]['previewed_instances'] ) ) {
+			return $original;
+		}
+
+		foreach ( self::$aggregated_multidimensionals[ $this->type ][ $id_base ]['previewed_instances'] as $previewed_setting ) {
+			// Skip applying previewed value for any settings that have already been applied.
+			if ( ! empty( self::$aggregated_multidimensionals[ $this->type ][ $id_base ]['preview_applied_instances'][ $previewed_setting->id ] ) ) {
+				continue;
+			}
+
+			// Do the replacements of the posted/default sub value into the root value.
+			$value = $previewed_setting->post_value( $previewed_setting->default );
+			$root = self::$aggregated_multidimensionals[ $previewed_setting->type ][ $id_base ]['root_value'];
+			$root = $previewed_setting->multidimensional_replace( $root, $previewed_setting->id_data['keys'], $value );
+			self::$aggregated_multidimensionals[ $previewed_setting->type ][ $id_base ]['root_value'] = $root;
+
+			// Mark this setting having been applied so that it will be skipped when the filter is called again.
+			self::$aggregated_multidimensionals[ $previewed_setting->type ][ $id_base ]['preview_applied_instances'][ $previewed_setting->id ] = true;
+		}
+
+		return self::$aggregated_multidimensionals[ $this->type ][ $id_base ]['root_value'];
 	}
 
 	/**
@@ -298,6 +465,57 @@ class WP_Customize_Setting {
 		return apply_filters( "customize_sanitize_{$this->id}", $value, $this );
 	}
 
+	/**
+	 * Get the root value for a setting, especially for multidimensional ones.
+	 *
+	 * @since 4.4.0
+	 * @access protected
+	 *
+	 * @param mixed $default Value to return if root does not exist.
+	 * @return mixed
+	 */
+	protected function get_root_value( $default = null ) {
+		$id_base = $this->id_data['base'];
+		if ( 'option' === $this->type ) {
+			return get_option( $id_base, $default );
+		} else if ( 'theme_mod' ) {
+			return get_theme_mod( $id_base, $default );
+		} else {
+			/*
+			 * Any WP_Customize_Setting subclass implementing aggregate multidimensional
+			 * will need to override this method to obtain the data from the appropriate
+			 * location.
+			 */
+			return $default;
+		}
+	}
+
+	/**
+	 * Set the root value for a setting, especially for multidimensional ones.
+	 *
+	 * @since 4.4.0
+	 * @access protected
+	 *
+	 * @param mixed $value Value to set as root of multidimensional setting.
+	 * @return bool Whether the multidimensional root was updated successfully.
+	 */
+	protected function set_root_value( $value ) {
+		$id_base = $this->id_data['base'];
+		if ( 'option' === $this->type ) {
+			return update_option( $id_base, $value );
+		} else if ( 'theme_mod' ) {
+			set_theme_mod( $id_base, $value );
+			return true;
+		} else {
+			/*
+			 * Any WP_Customize_Setting subclass implementing aggregate multidimensional
+			 * will need to override this method to obtain the data from the appropriate
+			 * location.
+			 */
+			return false;
+		}
+	}
+
 	/**
 	 * Save the value of the setting, using the related API.
 	 *
@@ -307,72 +525,52 @@ class WP_Customize_Setting {
 	 * @return bool The result of saving the value.
 	 */
 	protected function update( $value ) {
-		switch ( $this->type ) {
-			case 'theme_mod' :
-				$this->_update_theme_mod( $value );
-				return true;
+		$id_base = $this->id_data['base'];
+		if ( 'option' === $this->type || 'theme_mod' === $this->type ) {
+			if ( ! $this->is_multidimensional_aggregated ) {
+				return $this->set_root_value( $value );
+			} else {
+				$root = self::$aggregated_multidimensionals[ $this->type ][ $id_base ]['root_value'];
+				$root = $this->multidimensional_replace( $root, $this->id_data['keys'], $value );
+				self::$aggregated_multidimensionals[ $this->type ][ $id_base ]['root_value'] = $root;
+				return $this->set_root_value( $root );
+			}
+		} else {
+			/**
+			 * Fires when the {@see WP_Customize_Setting::update()} method is called for settings
+			 * not handled as theme_mods or options.
+			 *
+			 * The dynamic portion of the hook name, `$this->type`, refers to the type of setting.
+			 *
+			 * @since 3.4.0
+			 *
+			 * @param mixed                $value Value of the setting.
+			 * @param WP_Customize_Setting $this  WP_Customize_Setting instance.
+			 */
+			do_action( "customize_update_{$this->type}", $value, $this );
 
-			case 'option' :
-				return $this->_update_option( $value );
-
-			default :
-
-				/**
-				 * Fires when the {@see WP_Customize_Setting::update()} method is called for settings
-				 * not handled as theme_mods or options.
-				 *
-				 * The dynamic portion of the hook name, `$this->type`, refers to the type of setting.
-				 *
-				 * @since 3.4.0
-				 *
-				 * @param mixed                $value Value of the setting.
-				 * @param WP_Customize_Setting $this  WP_Customize_Setting instance.
-				 */
-				do_action( "customize_update_{$this->type}", $value, $this );
-
-				return has_action( "customize_update_{$this->type}" );
+			return has_action( "customize_update_{$this->type}" );
 		}
 	}
 
 	/**
-	 * Update the theme mod from the value of the parameter.
+	 * Deprecated method.
 	 *
 	 * @since 3.4.0
-	 *
-	 * @param mixed $value The value to update.
+	 * @deprecated 4.4.0 Deprecated in favor of update() method.
 	 */
-	protected function _update_theme_mod( $value ) {
-		// Handle non-array theme mod.
-		if ( empty( $this->id_data[ 'keys' ] ) ) {
-			set_theme_mod( $this->id_data[ 'base' ], $value );
-			return;
-		}
-		// Handle array-based theme mod.
-		$mods = get_theme_mod( $this->id_data[ 'base' ] );
-		$mods = $this->multidimensional_replace( $mods, $this->id_data[ 'keys' ], $value );
-		if ( isset( $mods ) ) {
-			set_theme_mod( $this->id_data[ 'base' ], $mods );
-		}
+	protected function _update_theme_mod() {
+		_deprecated_function( __METHOD__, '4.4.0', __CLASS__ . '::update()' );
 	}
 
 	/**
-	 * Update the option from the value of the setting.
+	 * Deprecated method.
 	 *
 	 * @since 3.4.0
-	 *
-	 * @param mixed $value The value to update.
-	 * @return bool The result of saving the value.
+	 * @deprecated 4.4.0 Deprecated in favor of update() method.
 	 */
-	protected function _update_option( $value ) {
-		// Handle non-array option.
-		if ( empty( $this->id_data[ 'keys' ] ) )
-			return update_option( $this->id_data[ 'base' ], $value );
-
-		// Handle array-based options.
-		$options = get_option( $this->id_data[ 'base' ] );
-		$options = $this->multidimensional_replace( $options, $this->id_data[ 'keys' ], $value );
-		if ( isset( $options ) )
-			return update_option( $this->id_data[ 'base' ], $options );
+	protected function _update_option() {
+		_deprecated_function( __METHOD__, '4.4.0', __CLASS__ . '::update()' );
 	}
 
 	/**
@@ -383,39 +581,33 @@ class WP_Customize_Setting {
 	 * @return mixed The value.
 	 */
 	public function value() {
-		// Get the callback that corresponds to the setting type.
-		switch( $this->type ) {
-			case 'theme_mod' :
-				$function = 'get_theme_mod';
-				break;
-			case 'option' :
-				$function = 'get_option';
-				break;
-			default :
+		$id_base = $this->id_data['base'];
+		$is_core_type = ( 'option' === $this->type || 'theme_mod' === $this->type );
 
-				/**
-				 * Filter a Customize setting value not handled as a theme_mod or option.
-				 *
-				 * The dynamic portion of the hook name, `$this->id_date['base']`, refers to
-				 * the base slug of the setting name.
-				 *
-				 * For settings handled as theme_mods or options, see those corresponding
-				 * functions for available hooks.
-				 *
-				 * @since 3.4.0
-				 *
-				 * @param mixed $default The setting default value. Default empty.
-				 */
-				return apply_filters( 'customize_value_' . $this->id_data[ 'base' ], $this->default );
+		if ( ! $is_core_type && ! $this->is_multidimensional_aggregated ) {
+			$value = $this->get_root_value( $this->default );
+
+			/**
+			 * Filter a Customize setting value not handled as a theme_mod or option.
+			 *
+			 * The dynamic portion of the hook name, `$this->id_date['base']`, refers to
+			 * the base slug of the setting name.
+			 *
+			 * For settings handled as theme_mods or options, see those corresponding
+			 * functions for available hooks.
+			 *
+			 * @since 3.4.0
+			 *
+			 * @param mixed $default The setting default value. Default empty.
+			 */
+			$value = apply_filters( "customize_value_{$id_base}", $value );
+		} else if ( $this->is_multidimensional_aggregated ) {
+			$root_value = self::$aggregated_multidimensionals[ $this->type ][ $id_base ]['root_value'];
+			$value = $this->multidimensional_get( $root_value, $this->id_data['keys'], $this->default );
+		} else {
+			$value = $this->get_root_value( $this->default );
 		}
-
-		// Handle non-array value
-		if ( empty( $this->id_data[ 'keys' ] ) )
-			return $function( $this->id_data[ 'base' ], $this->default );
-
-		// Handle array-based value
-		$values = $function( $this->id_data[ 'base' ] );
-		return $this->multidimensional_get( $values, $this->id_data[ 'keys' ], $this->default );
+		return $value;
 	}
 
 	/**
@@ -520,7 +712,7 @@ class WP_Customize_Setting {
 	 * @param $root
 	 * @param $keys
 	 * @param mixed $value The value to update.
-	 * @return
+	 * @return mixed
 	 */
 	final protected function multidimensional_replace( $root, $keys, $value ) {
 		if ( ! isset( $value ) )
@@ -853,7 +1045,7 @@ class WP_Customize_Nav_Menu_Item_Setting extends WP_Customize_Setting {
 	}
 
 	/**
-	 * Get the instance data for a given widget setting.
+	 * Get the instance data for a given nav_menu_item setting.
 	 *
 	 * @since 4.3.0
 	 * @access public
@@ -987,13 +1179,23 @@ class WP_Customize_Nav_Menu_Item_Setting extends WP_Customize_Setting {
 	 * Handle previewing the setting.
 	 *
 	 * @since 4.3.0
+	 * @since 4.4.0 Added boolean return value.
 	 * @access public
 	 *
 	 * @see WP_Customize_Manager::post_value()
+	 *
+	 * @return bool False if method short-circuited due to no-op.
 	 */
 	public function preview() {
 		if ( $this->is_previewed ) {
-			return;
+			return false;
+		}
+
+		$undefined = new stdClass();
+		$is_placeholder = ( $this->post_id < 0 );
+		$is_dirty = ( $undefined !== $this->post_value( $undefined ) );
+		if ( ! $is_placeholder && ! $is_dirty ) {
+			return false;
 		}
 
 		$this->is_previewed              = true;
@@ -1009,6 +1211,8 @@ class WP_Customize_Nav_Menu_Item_Setting extends WP_Customize_Setting {
 		}
 
 		// @todo Add get_post_metadata filters for plugins to add their data.
+
+		return true;
 	}
 
 	/**
@@ -1621,13 +1825,23 @@ class WP_Customize_Nav_Menu_Setting extends WP_Customize_Setting {
 	 * Handle previewing the setting.
 	 *
 	 * @since 4.3.0
+	 * @since 4.4.0 Added boolean return value
 	 * @access public
 	 *
 	 * @see WP_Customize_Manager::post_value()
+	 *
+	 * @return bool False if method short-circuited due to no-op.
 	 */
 	public function preview() {
 		if ( $this->is_previewed ) {
-			return;
+			return false;
+		}
+
+		$undefined = new stdClass();
+		$is_placeholder = ( $this->term_id < 0 );
+		$is_dirty = ( $undefined !== $this->post_value( $undefined ) );
+		if ( ! $is_placeholder && ! $is_dirty ) {
+			return false;
 		}
 
 		$this->is_previewed       = true;
@@ -1638,6 +1852,8 @@ class WP_Customize_Nav_Menu_Setting extends WP_Customize_Setting {
 		add_filter( 'wp_get_nav_menu_object', array( $this, 'filter_wp_get_nav_menu_object' ), 10, 2 );
 		add_filter( 'default_option_nav_menu_options', array( $this, 'filter_nav_menu_options' ) );
 		add_filter( 'option_nav_menu_options', array( $this, 'filter_nav_menu_options' ) );
+
+		return true;
 	}
 
 	/**
diff --git a/tests/phpunit/tests/customize/setting.php b/tests/phpunit/tests/customize/setting.php
index 069a8ae1b0..600fb3faa9 100644
--- a/tests/phpunit/tests/customize/setting.php
+++ b/tests/phpunit/tests/customize/setting.php
@@ -102,7 +102,7 @@ class Tests_WP_Customize_Setting extends WP_UnitTestCase {
 			$setting = new WP_Customize_Setting( $this->manager, $name, compact( 'type', 'default' ) );
 			$this->assertEquals( $this->undefined, call_user_func( $type_options['getter'], $name, $this->undefined ) );
 			$this->assertEquals( $default, $setting->value() );
-			$setting->preview();
+			$this->assertTrue( $setting->preview(), 'Preview should not no-op since setting has no existing value.' );
 			$this->assertEquals( $default, call_user_func( $type_options['getter'], $name, $this->undefined ), sprintf( 'Expected %s(%s) to return setting default: %s.', $type_options['getter'], $name, $default ) );
 			$this->assertEquals( $default, $setting->value() );
 
@@ -114,18 +114,18 @@ class Tests_WP_Customize_Setting extends WP_UnitTestCase {
 			$setting = new WP_Customize_Setting( $this->manager, $name, compact( 'type', 'default' ) );
 			$this->assertEquals( $initial_value, call_user_func( $type_options['getter'], $name ) );
 			$this->assertEquals( $initial_value, $setting->value() );
-			$setting->preview();
+			$this->assertFalse( $setting->preview(), 'Preview should no-op since setting value was extant and no post value was present.' );
 			$this->assertEquals( 0, did_action( "customize_preview_{$setting->id}" ) ); // only applicable for custom types (not options or theme_mods)
 			$this->assertEquals( 0, did_action( "customize_preview_{$setting->type}" ) ); // only applicable for custom types (not options or theme_mods)
 			$this->assertEquals( $initial_value, call_user_func( $type_options['getter'], $name ) );
 			$this->assertEquals( $initial_value, $setting->value() );
 
-			// @todo What if we call the setter after preview() is called? If no post_value, should the new set value be stored? If that happens, then the following 3 assertions should be inverted
 			$overridden_value = "overridden_value_$name";
 			call_user_func( $type_options['setter'], $name, $overridden_value );
-			$this->assertEquals( $initial_value, call_user_func( $type_options['getter'], $name ) );
-			$this->assertEquals( $initial_value, $setting->value() );
-			$this->assertNotEquals( $overridden_value, $setting->value() );
+			$message = 'Initial value should be overridden because initial preview() was no-op due to setting having existing value and/or post value was absent.';
+			$this->assertEquals( $overridden_value, call_user_func( $type_options['getter'], $name ), $message );
+			$this->assertEquals( $overridden_value, $setting->value(), $message );
+			$this->assertNotEquals( $initial_value, $setting->value(), $message );
 
 			// Non-multidimensional: Test unset setting being overridden by a post value
 			$name = "unset_{$type}_overridden";
@@ -133,7 +133,7 @@ class Tests_WP_Customize_Setting extends WP_UnitTestCase {
 			$setting = new WP_Customize_Setting( $this->manager, $name, compact( 'type', 'default' ) );
 			$this->assertEquals( $this->undefined, call_user_func( $type_options['getter'], $name, $this->undefined ) );
 			$this->assertEquals( $default, $setting->value() );
-			$setting->preview(); // activate post_data
+			$this->assertTrue( $setting->preview(), 'Preview applies because setting has post_data_overrides.' ); // activate post_data
 			$this->assertEquals( $this->post_data_overrides[ $name ], call_user_func( $type_options['getter'], $name, $this->undefined ) );
 			$this->assertEquals( $this->post_data_overrides[ $name ], $setting->value() );
 
@@ -145,7 +145,7 @@ class Tests_WP_Customize_Setting extends WP_UnitTestCase {
 			$setting = new WP_Customize_Setting( $this->manager, $name, compact( 'type', 'default' ) );
 			$this->assertEquals( $initial_value, call_user_func( $type_options['getter'], $name, $this->undefined ) );
 			$this->assertEquals( $initial_value, $setting->value() );
-			$setting->preview(); // activate post_data
+			$this->assertTrue( $setting->preview(), 'Preview applies because setting has post_data_overrides.' ); // activate post_data
 			$this->assertEquals( 0, did_action( "customize_preview_{$setting->id}" ) ); // only applicable for custom types (not options or theme_mods)
 			$this->assertEquals( 0, did_action( "customize_preview_{$setting->type}" ) ); // only applicable for custom types (not options or theme_mods)
 			$this->assertEquals( $this->post_data_overrides[ $name ], call_user_func( $type_options['getter'], $name, $this->undefined ) );
@@ -167,7 +167,7 @@ class Tests_WP_Customize_Setting extends WP_UnitTestCase {
 			$setting = new WP_Customize_Setting( $this->manager, $name, compact( 'type', 'default' ) );
 			$this->assertEquals( $this->undefined, call_user_func( $type_options['getter'], $base_name, $this->undefined ) );
 			$this->assertEquals( $default, $setting->value() );
-			$setting->preview();
+			$this->assertTrue( $setting->preview() );
 			$base_value = call_user_func( $type_options['getter'], $base_name, $this->undefined );
 			$this->assertArrayHasKey( 'foo', $base_value );
 			$this->assertEquals( $default, $base_value['foo'] );
@@ -311,8 +311,8 @@ class Tests_WP_Customize_Setting extends WP_UnitTestCase {
 		$this->assertEquals( $initial_value, $this->custom_type_getter( $name, $this->undefined ) );
 		$this->assertEquals( $initial_value, $setting->value() );
 		$setting->preview();
-		$this->assertEquals( 1, did_action( "customize_preview_{$setting->id}" ) );
-		$this->assertEquals( 2, did_action( "customize_preview_{$setting->type}" ) );
+		$this->assertEquals( 0, did_action( "customize_preview_{$setting->id}" ), 'Zero preview actions because initial value is set with no incoming post value, so there is no preview to apply.' );
+		$this->assertEquals( 1, did_action( "customize_preview_{$setting->type}" ) );
 		$this->assertEquals( $initial_value, $this->custom_type_getter( $name, $this->undefined ) ); // should be same as above
 		$this->assertEquals( $initial_value, $setting->value() ); // should be same as above
 
@@ -325,8 +325,8 @@ class Tests_WP_Customize_Setting extends WP_UnitTestCase {
 		$this->assertEquals( $this->undefined, $this->custom_type_getter( $name, $this->undefined ) );
 		$this->assertEquals( $default, $setting->value() );
 		$setting->preview();
-		$this->assertEquals( 1, did_action( "customize_preview_{$setting->id}" ) );
-		$this->assertEquals( 3, did_action( "customize_preview_{$setting->type}" ) );
+		$this->assertEquals( 1, did_action( "customize_preview_{$setting->id}" ), 'One preview action now because initial value was not set and/or there is no incoming post value, so there is is a preview to apply.' );
+		$this->assertEquals( 2, did_action( "customize_preview_{$setting->type}" ) );
 		$this->assertEquals( $post_data_overrides[ $name ], $this->custom_type_getter( $name, $this->undefined ) );
 		$this->assertEquals( $post_data_overrides[ $name ], $setting->value() );
 
@@ -342,7 +342,7 @@ class Tests_WP_Customize_Setting extends WP_UnitTestCase {
 		$this->assertEquals( $initial_value, $setting->value() );
 		$setting->preview();
 		$this->assertEquals( 1, did_action( "customize_preview_{$setting->id}" ) );
-		$this->assertEquals( 4, did_action( "customize_preview_{$setting->type}" ) );
+		$this->assertEquals( 3, did_action( "customize_preview_{$setting->type}" ) );
 		$this->assertEquals( $post_data_overrides[ $name ], $this->custom_type_getter( $name, $this->undefined ) );
 		$this->assertEquals( $post_data_overrides[ $name ], $setting->value() );