Haven't seen this mentioned and maybe there's something I'm missing but... Started new game. Playing around with wizard skills - killing the other character gets you both xp. However...
If you kill both characters at the same time (ie with a fireball), seems to be stuck in combat with them both dead - and there's no 'game over' or restart or anything. Just both character portraits sit there with a skull beside them and nothing ever seems to advance from there - only option was to quit out and restart the game entirely.