I tested in IE6, FF2 on Mac and PC and wasn't able to replicate the problem. One thing I did notice is that it appears that, rather than simply opening the menus, it looks like when you click on the menus, it follows the link. It also looks like there might be a configuration problem with the open on click. You might want to check out this documentation...
http://www.udm4.com/manual/setup/onclick/
Hope this helps.