Compared to other bugs I've just read through, this is a small one.
If you challenge a Pub Visitor to a Duel (Fist-fight) while you have less than full health, you will insta heal up to full health before the start of the fight where and will return to (full health) after the fight.
So unlike arena modes in Warband where you start, and are returned to whatever your actual amount of hp should be at, a small exploit to get to full health.