Index: wp-includes/formatting.php
===================================================================
--- wp-includes/formatting.php	(revision 6300)
+++ wp-includes/formatting.php	(working copy)
@@ -323,9 +323,8 @@
 	$title = strip_tags($title);
 	$title = apply_filters('sanitize_title', $title);
 
-	if (empty($title)) {
+	if ( '' === $title || false === $title )
 		$title = $fallback_title;
-	}
 
 	return $title;
 }
Index: wp-includes/taxonomy.php
===================================================================
--- wp-includes/taxonomy.php	(revision 6300)
+++ wp-includes/taxonomy.php	(working copy)
@@ -699,7 +699,7 @@
 			return 0;
 		$where = $wpdb->prepare( "t.term_id = %d", $term );
 	} else {
-		if ( ! $term = sanitize_title($term) )
+		if ( '' === $term = sanitize_title($term) )
 			return 0;
 		$where = $wpdb->prepare( "t.slug = %s", $term );
 	}