[Zope] is this a browser problem?

On each member's "Change User" screen in acl_users, I can only seem to select one role at a time from the menu, or use shift-click to choose adjacent roles. This is using Mozilla (linux.9.3), Konqueror, IE(MacOSX) and Omniweb. Also, the menu to remove roles only brings up one or two roles or nothing? Can I change these by hand somewhere? Anyone else have this problem? --Tom