Index: wp-includes/default-widgets.php
===================================================================
--- wp-includes/default-widgets.php	(revision 14459)
+++ wp-includes/default-widgets.php	(working copy)
@@ -1057,7 +1057,7 @@
 
 		echo $args['before_widget'];
 
-		if ( isset($instance['title']) )
+		if ( !empty($instance['title']) )
 			echo $args['before_title'] . $instance['title'] . $args['after_title'];
 
 		wp_nav_menu( array( 'menu' => $nav_menu ) );