diff --git a/TODO b/TODO
index c0688602..d9f4a5f3 100644
--- a/TODO
+++ b/TODO
@@ -1,10 +1,13 @@
-- vipsthumbnail -t plus large -s seems to fail?
+- try:
 
-  change caching:
+	$ vipsthumbnail Chicago.png --vips-concurrency=1
+	memory: high-water mark 180.57 MB
+	$ vipsthumbnail Chicago.png --vips-concurrency=4
+	memory: high-water mark 180.57 MB
 
-  - autorotate should make a mem copy if it find rotation is necessary
+  shouldn't memuse drop with concurrency 1?
 
-  - remove second vips_cache()
+- bicubic adds noise to 255/255/255, why? try babe.jpg background
 
 - experiment with size down to two sizes above in vipsthumbnail
 
@@ -18,7 +21,6 @@
 
 
 
-- bicubic adds noise to 255/255/255, why? try babe.jpg background
 
 
 
diff --git a/libvips/foreign/vipspng.c b/libvips/foreign/vipspng.c
index d40faa86..c3a36f56 100644
--- a/libvips/foreign/vipspng.c
+++ b/libvips/foreign/vipspng.c
@@ -862,7 +862,7 @@ write_vips( Write *write, int compress, int interlace )
 	/* Write data.
 	 */
 	for( i = 0; i < nb_passes; i++ ) 
-		if( vips_sink_disc( write->in, write_png_block, write ) )
+		if( vips_sink_disc( in, write_png_block, write ) )
 			return( -1 );
 
 	/* The setjmp() was held by our background writer: reset it.
diff --git a/libvips/iofuncs/image.c b/libvips/iofuncs/image.c
index 10972f26..a8b7e6ab 100644
--- a/libvips/iofuncs/image.c
+++ b/libvips/iofuncs/image.c
@@ -2781,6 +2781,24 @@ vips_image_wio_input( VipsImage *image )
 		 */
 		g_object_unref( t1 );
 
+		/* We need to zap any start/gen/stop callbacks. If we don't,
+		 * calling vips_region_prepare_to() later to read from this 
+		 * image will fail, since it will think it need to create the
+		 * image, not read from it.
+		 */
+		image->start_fn = NULL;
+		image->generate_fn = NULL;
+		image->stop_fn = NULL;
+		image->client1 = NULL;
+		image->client2 = NULL;
+
+		/* ... and that may confuse any regions which are trying to
+		 * generate from this image.
+		 */
+		if( image->regions ) 
+			vips_warn( "vips_image_wio_input", "%s",
+				"rewinding image with active regions" ); 
+
 		break;
 
 	case VIPS_IMAGE_OPENIN:
diff --git a/tools/vipsthumbnail.c b/tools/vipsthumbnail.c
index ab411e7d..c9925265 100644
--- a/tools/vipsthumbnail.c
+++ b/tools/vipsthumbnail.c
@@ -570,12 +570,18 @@ thumbnail_crop( VipsObject *process, VipsImage *im )
 static VipsImage *
 thumbnail_rotate( VipsObject *process, VipsImage *im )
 {
-	VipsImage **t = (VipsImage **) vips_object_local_array( process, 1 );
+	VipsImage **t = (VipsImage **) vips_object_local_array( process, 2 );
+	VipsAngle angle = get_angle( im );
 
-	if( rotate_image ) {
-		if( vips_rot( im, &t[0], get_angle( im ), NULL ) )
+	if( rotate_image &&
+		angle != VIPS_ANGLE_0 ) {
+		/* Need to copy to memory, we have to stay seq.
+		 */
+		t[0] = vips_image_new_memory();
+		if( vips_image_write( im, t[0] ) ||
+			vips_rot( t[0], &t[1], angle, NULL ) )
 			return( NULL ); 
-		im = t[0];
+		im = t[1];
 
 		(void) vips_image_remove( im, ORIENTATION );
 	}
@@ -589,8 +595,6 @@ thumbnail_rotate( VipsObject *process, VipsImage *im )
 static int
 thumbnail_write( VipsObject *process, VipsImage *im, const char *filename )
 {
-	VipsImage **t = (VipsImage **) vips_object_local_array( process, 1 );
-
 	char *file;
 	char *p;
 	char buf[FILENAME_MAX];
@@ -622,16 +626,7 @@ thumbnail_write( VipsObject *process, VipsImage *im, const char *filename )
 
 	g_free( file );
 
-	/* We need to cache the whole of the thumbnail before we write it 
-	 * in case we are writing an interlaced image. Interlaced png (for
-	 * example) will make 7 passes over the image during write.
-	 */
-	if( vips_tilecache( im, &t[0], 
-		"threaded", TRUE,
-		"persistent", TRUE,
-		"max_tiles", -1,
-		NULL ) ||
-		vips_image_write_to_file( t[0], output_name, NULL ) ) {
+	if( vips_image_write_to_file( im, output_name, NULL ) ) {
 		g_free( output_name );
 		return( -1 );
 	}