In game #5623879, a possession game with donate, I decide turn (I don't know) when I have 3 farm village and two possession to buy a donate to erase all my card except a province the farm village and the possession.
A few turn later my opponent do the same thing.
So we were in the case or the game cannot finish.
So no one can say I win and no one accept to say I loose.
A button "Offer Tie" or Pat (like in chess) would be the solution.