Help with Doom 3 AA settings

[dario03]

For some reason when I turn the Antialiasing settings to 8x or 16x in Doom 3 it automatically lowers the resolution to 640x480 and turns off AA. I assume my system is capable of running at these settings because at 4x AA I maintain 60fps without stressing my vid card.
Why is it doing this and more importantly how can I make it work right?

 

[<[MaTT]>]

Does that to me too i think its screwed up, i just have res and 4x
AA.