Index: wp-includes/post.php
===================================================================
--- wp-includes/post.php	(revision 17094)
+++ wp-includes/post.php	(working copy)
@@ -2510,7 +2510,8 @@
 		$post_parent = 0;
 
 	// Check the post_parent to see if it will cause a hierarchy loop
-	$post_parent = apply_filters( 'wp_insert_post_parent', $post_parent, $post_ID, compact( array_keys( $postarr ) ), $postarr );
+	if ( 'revision' != $post->post_type )
+		$post_parent = apply_filters( 'wp_insert_post_parent', $post_parent, $post_ID, compact( array_keys( $postarr ) ), $postarr );
 
 	if ( isset($menu_order) )
 		$menu_order = (int) $menu_order;