Index: wp-includes/wp-db.php
===================================================================
--- wp-includes/wp-db.php	(revision 12600)
+++ wp-includes/wp-db.php	(working copy)
@@ -1109,7 +1109,7 @@
 
 		$bt = array_reverse( $bt );
 		foreach ( (array) $bt as $call ) {
-			if ( @$call['class'] == __CLASS__ )
+			if ( isset($call['class']) && (__CLASS__ == $call['class']) )
 				continue;
 			$function = $call['function'];
 			if ( isset( $call['class'] ) )