Friendly AI taking over my core provinces?

I'm currently in a Classic Dawn of the Patriot game, where 1/3 of the players automatically have share map from the start. As per usual some players go afk, now, over a week into the game I'm practicly steamrolling it, when at daychange today, all of a sudden one of my core provinces (which was att 70% morale mind you) got randomly taken over by a neighbouring friendly AI.

This is BEYOND stupid! I can't get this province back in this game mode, to make matters worse it's a province producing goods.

In addition to this stupidity, two more, although not resource-producing provinces of mine also "rebelled" against me and joined the same friendly AI, those were not core provinces however, but they were also at 70% morale. I have NEVER seen this before. Sure, I've lost provinces with low morale that were recently conquered and/or not guarded by troops before, but CORE provinces with an overall positive morale!? By a friendly AI!? Never. I can use those resources WAY better than a goddamn computer.

What is this sorcery?!