Nothing inside the chipset should be decoding port 80 writes. It's possible this board has a port 80 decoder wired onto the board that's misbehaving. I've seen other laptop boards with port 80 decoders
wired onto the board, even if the 7 segment display is only populated
on debug builds.
We use PCI port 80 decoders internally for debugging quite often, so if there were some chipset issue related to port 80 it would have showed up a long time ago, and this is the first I've heard of
hangs related to port 80 writes.