[Zope] ZCatalog and permissions

Hi there, I'm using a ZCatalog in Zope 2.1 to catalog a site. I set it so that it would only catalog objects where Anonymous has permission 'access contents information'. If I do that, however, it doesn't seem to work right. Only a few objects (if any) get catalogued, instead of all of them. Can anyone explain? Or is this a bug? Regards, Martijn