Index: includes/menu.inc
===================================================================
RCS file: /cvs/drupal/drupal/includes/menu.inc,v
retrieving revision 1.406
diff -u -p -r1.406 menu.inc
--- includes/menu.inc	22 Aug 2010 14:57:44 -0000	1.406
+++ includes/menu.inc	23 Aug 2010 13:04:27 -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__' . str_replace('-', '_', $data['link']['menu_name']);
   }
 
   return $build;