Index: wp-includes/query.php
===================================================================
--- wp-includes/query.php	(revision 17632)
+++ wp-includes/query.php	(working copy)
@@ -2465,7 +2465,7 @@
 		}
 
 		// Parse the meta query again if query vars have changed.
-		if ( $this->query_vars_changed ) {
+		if ( $this->query_vars_changed && isset( $q['meta_query'] ) ) {
 			$meta_query_hash = md5( serialize( $q['meta_query'] ) );
 			$_meta_query = $q['meta_query'];
 			unset( $q['meta_query'] );