I met with Christoffer Malamart after blowing my way through 3 levels of dungeon (lightning makes this game go from extremely challenging to relatively easy), and during the combat he approached me and convinced me of his innocence, even penning a letter to the Cardinal in Alvaron.

However he and his goons continue to attack me after the dialogue, even though he directed me to talk to Inquisitor Nicolas (who happily chucks spell after spell at me).

Is this a bug? A gamestopper? How do I make these guys stop attacking me?

I tried that. And got cut to ribbons by all the attackers.

You must have auto-save conversation with malamart.Load it and complete the conversation.Go out of portal then get back in try it again ,if not works then go other town and then get back to citadel again.

I've tried that... didn't work. I've actually progressed since then to Alvorn and met with Cardinal Letti, arrested numerous heretics but still the GM and his cronies attack the minute you return to the citadel level.

I had a similar bug, turned out it was because an area effect spell had hit Malamart and in that case he never deaggros. However his goons did stop attacking.

But maybe someone can confirm whether you need to talk to him again. I've been slaying fallen angels and it doesn't seem so.

Hmm weird..Then one more thing left ,kill the guards and malamart.I mean did enough dmg until his hp goes 0 (you cant kill him exactly) So point is ; get rid of bug..After you done go out of citadel and get in.P.S: Use some magical boxes to help you on attack