I don't get it either, sorry. Why would it be a "serious bug" that you can't get horses in a house? People have the right to be polite, after all, and not gallop through other people's living room, not even in war. Let's keep civil, even the military.

Really, I've seen this "bug" before, in MTW and RTW, where cavalry could not climb ladders during a siege. They couldn't even man (err, horse?) a ram, as well. Horses can be quite stuborn creatures. We're lucky TW doesn't feature asses, after all, now these are really stuborn, I hear. Equus africanus asinus, that is, not the other... you know.