Well, is it really an ATI bug... or a shortcoming of the hardware.
You are after all supposed to use DisplayPort monitors for the perfect Eyefinity experience, the adapters are really just a workaround.
So maybe it's just the adapters that are limited, and you should be on to their manufacturers...?
Btw, are you using passive or active? I think the active ones are supposed to support higher res (and perhaps higher refresh rates)