Index: includes/menu.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/menu.inc,v
retrieving revision 1.407
diff -u -p -r1.407 menu.inc
--- includes/menu.inc	23 Aug 2010 23:38:06 -0000	1.407
+++ includes/menu.inc	26 Aug 2010 07:45:12 -0000
@@ -961,7 +961,7 @@ function menu_tree_output($tree) {
     $build['#sorted'] = TRUE;
     // Add the theme wrapper for outer markup.
     // Allow menu-specific theme overrides.
-    $build['#theme_wrappers'][] = 'menu_tree__' . $data['link']['menu_name'];
+    $build['#theme_wrappers'][] = 'menu_tree__' . strtr($data['link']['menu_name'], '-', '_');
   }
 
   return $build;