Index: wp-includes/default-widgets.php
===================================================================
--- wp-includes/default-widgets.php	(revision 18636)
+++ wp-includes/default-widgets.php	(working copy)
@@ -177,7 +177,7 @@
 
 	function widget( $args, $instance ) {
 		extract($args);
-		$title = apply_filters('widget_title', $instance['title'], $instance, $this->id_base);
+		$title = apply_filters( 'widget_title', empty( $instance['title'] ) ? '' : $instance['title'], $instance, $this->id_base );
 
 		echo $before_widget;
 		if ( $title )
@@ -1064,7 +1064,7 @@
 		if ( !$nav_menu )
 			return;
 
-		$instance['title'] = apply_filters('widget_title', $instance['title'], $instance, $this->id_base);
+		$instance['title'] = apply_filters( 'widget_title', empty( $instance['title'] ) ? '' : $instance['title'], $instance, $this->id_base );
 
 		echo $args['before_widget'];