Index: wp-includes/taxonomy.php
===================================================================
--- wp-includes/taxonomy.php	(Revision 19161)
+++ wp-includes/taxonomy.php	(Arbeitskopie)
@@ -617,7 +617,7 @@
 		$orderby = 't.slug';
 	else if ( 'term_group' == $orderby )
 		$orderby = 't.term_group';
-	else
+	else if (!isset($orderby))
 		$orderby = 't.term_id';
 
 	$where = '';