Index: includes/menu.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/menu.inc,v
retrieving revision 1.431
diff -u -p -r1.431 menu.inc
--- includes/menu.inc	4 Jan 2011 06:20:30 -0000	1.431
+++ includes/menu.inc	8 Feb 2011 05:14:05 -0000
@@ -1042,7 +1042,7 @@ function menu_tree_output($tree) {
     }
 
     // Allow menu-specific theme overrides.
-    $element['#theme'] = 'menu_link__' . $data['link']['menu_name'];
+    $element['#theme'] = 'menu_link__' . strtr($data['link']['menu_name'], '-', '_');
     $element['#attributes']['class'] = $class;
     $element['#title'] = $data['link']['title'];
     $element['#href'] = $data['link']['href'];