Index: modules/system/system.admin.inc
===================================================================
RCS file: /cvs/drupal/drupal/modules/system/system.admin.inc,v
retrieving revision 1.258
diff -u -p -r1.258 system.admin.inc
--- modules/system/system.admin.inc	7 Feb 2010 17:29:09 -0000	1.258
+++ modules/system/system.admin.inc	11 Feb 2010 06:59:27 -0000
@@ -444,6 +444,7 @@ function system_theme_default() {
     else {
       drupal_set_message(t('The %theme theme was not found.', array('%theme' => $theme)), 'error');
     }
+    menu_rebuild();
     drupal_goto('admin/appearance');
   }
   return drupal_access_denied();