Index: class-wp-image-editor-gd.php
===================================================================
--- class-wp-image-editor-gd.php	(revision 30729)
+++ class-wp-image-editor-gd.php	(working copy)
@@ -306,9 +306,12 @@
 	 */
 	public function rotate( $angle ) {
 		if ( function_exists('imagerotate') ) {
-			$rotated = imagerotate( $this->image, $angle, 0 );
+			$transparency = imagecolorallocatealpha( $this->image, 255, 255, 255, 127 );
+			$rotated = imagerotate( $this->image, $angle, $transparency );
 
 			if ( is_resource( $rotated ) ) {
+				imagealphablending($rotated, true);
+				imagesavealpha($rotated, true);
 				imagedestroy( $this->image );
 				$this->image = $rotated;
 				$this->update_size();