Index: classes.php
===================================================================
--- classes.php	(revision 15434)
+++ classes.php	(working copy)
@@ -1190,6 +1190,7 @@
 		$css_class = array('page_item', 'page-item-'.$page->ID);
 		if ( !empty($current_page) ) {
 			$_current_page = get_page( $current_page );
+			_get_post_ancestors($_current_page);
 			if ( isset($_current_page->ancestors) && in_array($page->ID, (array) $_current_page->ancestors) )
 				$css_class[] = 'current_page_ancestor';
 			if ( $page->ID == $current_page )