The part's designed for PCI-E in the first place and they add a PCI-E to AGP bridge part on the AGP card- of which, many people seem to have all sorts of pain from with fglrx in the first place.
This is actually funny , the problem has to do only with the drivers because on the windows side after 7.7 drivers no driver work, so they screw things up with agp cards.
And the best part is in the 8.42.3 release notes :
Segmentation faults in OpenGL applications and the ATI Catalyst™ Control Center Linux Edition with Rialto-based AGP cards no longer occur.
I don't know really what else is there to tell , but if the ATI beta testers use only PCI-E cards , like Phonorix do , there will be no fix beacause this sort of problems will never be reported back to ATI.
PCI-E is actually a much better thing from start to finish, but that's short shrift for all the poor folks stuck with AGP right now. (I'm sure someone will tell you "just upgrade"... Heh... I'm just NOW upgrading my 5 year old test farm hardware with Junk PC's slapped together from bargain bin stuff from Fry's right now- don't ask why... >:-) Both the attitude that you'll find from the vendors and my not having the nice hardware are sore subjects right at the moment :D )