[Zope-dev] getRoles()

I was fooling around in AccessControl\User.py, tying to add some user groups from an NT domain in the getRoles() method. Why does the getRoles() method get called so many times? Seems like once for each object on a page that needs authentication? Was making for a VERY slow page load while my NT Domain was across a slow WAN link. I would have thought it would have been called once and then cached, or...? thanks for any insight.