You only die twice

Platform: PC

Do you have any mods? No mods.

Please explain the issue is in as much detail as possible:

I had a strange bug when playing Kingmaker.
I was fighting Ivoretti in his palace.
It started normal: I hurt him, he summons naga, I kill naga and hit him again.
Then comes his dialogue. I chose the neutral (or chaotic neutral?) answer to kill him.
But then he continues fighting. I beat him againand I see the same dialogue and this time I chose the chaotic good option to let him live. He kills himself then, I kill the remaining enemies and the battle ends.

So far this bug did not cause much trouble, but I got the event to investigate the curse of the briar twice.