Index: post.php
===================================================================
--- post.php	(revision 17369)
+++ post.php	(working copy)
@@ -3796,7 +3796,10 @@
 
 	$data = apply_filters( 'wp_update_attachment_metadata', $data, $post->ID );
 
-	return update_post_meta( $post->ID, '_wp_attachment_metadata', $data);
+	if ( ! empty($data) )
+		return update_post_meta( $post->ID, '_wp_attachment_metadata', $data );
+
+	return false;
 }
 
 /**