JS error: leaf items get onclick expander

If you click a menu item that is not a tree, Firebug will report an error (right before the page changes to go to your requested click) about "elem" not having properties or being defined, or some such. Adding in breakpoints suggests line 27:

   Drupal.dhtmlMenu.switchMenu($('#'+ id)[0], $(this).parents()[0]);

I suspect doing something like "if clicked menu has class 'leaf', don't fire." would solve this.