game #1807894 on frankfurt
Just after I had Possessed my opponent a bunch, he played a Count and then requested an undo which would not take him back into the possessed turn, just back to the Count choice. I granted it. Then I was looking at his hand, he requested an undo again but for me it said "Undo request pending" as if I had requested an undo. I could not grant his undo but I could cancel (not decline). Which I did, then my opponent requested an undo again. I cancelled. I don't know if my opponent could do anything at that point or not but he then resigned.
I was the opponent. After a couple of tries without any consequences ("pending undo request" even though he granted it) I cancelled the undo request. I was able to play my Treasures but I couldn't buy anything then. (So I resigned.)