Ok, you didn't mention the model number, so we couldn't see this is something new. A quick check turned out that this bridge is used on many other mainboards from different vendors to provide e.g. USB3 functionality. Since I heard nothing contrary, I guess it isn't that all these mainboards do have problems with 64-bit Linux ...
Seems again more an unique issue from Asus, for which I do know them and honestly don't buy'em ...
Regards
fnu