Game # 139446996
User asked for an undo, I allowed it, and the game reset to the beginning. The user seemed to expect it, and I was winning handily at the time.
Not sure what happened, whether it was somehow deliberate or not.
I guess it was deliberate, some players try this on unsuspecting opponents. When an opponent asks for an undo, always check where they want to undo to. This is indicated in the log to your right by a yellow border. In the benign example below, it means they want to undo buying the Inn.
(https://i.imgur.com/xtblOto.png)
Normally players want to undo 1 or 2 steps, sometimes to the end of their turn (you can also see the number steps they want to undo in box that asks you to grant or deny the undo). If it's for many more steps (like 20+), and you can't see in the log where it would lead to, deny the undo or ask them in chat what they want to do.
Heh. The user was a 54+ rating, and was losing to me (49-50). Probably didn't like it, and used my ignorance to reset the game to the beginning.