+/**
+ * Prevents a menu item ID from being used more than once.
+ *
+ * @since 3.0.1
+ * @access private
+ */
+function _nav_menu_item_id_use_once( $id, $item ) {
+ static $_used_ids = array();
+ if ( in_array( $item->ID, $_used_ids ) )
+ return '';
+ $_used_ids[] = $item->ID;
+ return $id;
+}
+add_filter( 'nav_menu_item_id', '_nav_menu_item_id_use_once', 10, 2 );
+