Index: wp-includes/post.php
===================================================================
--- wp-includes/post.php	(revision 22230)
+++ wp-includes/post.php	(working copy)
@@ -2936,7 +2936,9 @@
 		$feeds = array();
 
 	$hierarchical_post_types = get_post_types( array('hierarchical' => true) );
-	if ( 'attachment' == $post_type ) {
+	if ( 'nav_menu_item' == $post_type ) {
+		return $slug;
+	} elseif ( 'attachment' == $post_type ) {
 		// Attachment slugs must be unique across all types.
 		$check_sql = "SELECT post_name FROM $wpdb->posts WHERE post_name = %s AND ID != %d LIMIT 1";
 		$post_name_check = $wpdb->get_var( $wpdb->prepare( $check_sql, $slug, $post_ID ) );