I found two problems with Dorn;
1) I met his necromancer friend Krynn in the wilderness and killed the hell out of her, then had a talk with Dorn. After this conversation, he and my character break whatever command they have every 2 seconds to stare at eachother, making walking around basicly impossible. It looks like they want to engage in conversation but there is no conversation to be had (Dorn has nothing to say to you). This behavior persists after quicksaving and loading and after several times of killing her. The only way to prevent it is to not kill Krynn and take her letter.
You talk to Krynn, kill her, take her letter and talk to Dorn, then the characters no longer have a talking script running.
2) Dorn is a paladin kit, but has 8hp at level 1.
Paladins have d10 Hitdice so he should have max HP, ten at level one, not eight.
On a non-bug-but-weird-sidenote; he's the Butcher of Luskan, ran with a mercenary company and tracked his fellows a year. He has 0 XP when he joins you, being way behind on other partymembers by that time of the game while being inconsistent with his backstory.
He should have some experience under his belt, let's say juuust enough to hit level 2. Currently, he's more clueless than Charname when she leaves Candlekeep.