https://www.warlight.net/MultiPlayer?GameID=13629488

The AI noticed he was only missing those 3 territories which he could use better then his teammate since he would have the full Partha bonus at that point so decided it would be better to take those 3 territories away from his teammate (not thinking about the consequences of eliminating him).

Yes AI are pretty stupid after all in this game but any decently skilled player in this game knows that.

I think the AI made a good choice there.

Problems that should be fixable for the AI is that the AI plays sanction cards based on alphabetical name order and that AI's prioritize attacking neutrals too much.