I just played a game with this player who repeatedly requested undo after his turn ended and my turn had started. I did not even know this was possible.
Anyway I denied of course, but why allow this at all? In this case it was just used as a form of abusive behaviour.
(http://i293.photobucket.com/albums/mm50/gamerdadx/6657f6bd-d628-44d2-b9ec-12f1443d77e8.png)
Undo should never even be allowed when you've gotten new information, such as after drawing a card. Maybe it could be a setting that both players have to agree on before the game, but having this is as the default setting is crazy. I have players getting annoyed at me because I don't grant them undo in these cases. Add to that the fact that the log is missing some performed actions, so that sometimes it looks like they want to undo a card draw, but it's actually a legitimate undo request.
be careful of glitches too. You can buy cards without actually hitting the button to play treasures or use tokens. In some cases I have bought a card using tokens without clicking on 'use token' or whatever. Sometimes it will freeze up. This recently happened in a game where i was pretty far ahead and may even have bought the last province (don't recall). I bought the card without hitting 'use token', game froze, I requested undo and he just ignored me. I had to resign or he would have been given the option to force me to resign. Ridiculous since i still won technically...
If you have Autobuy enabled in the options, the game will take your coin tokens into account when deciding which cards you can buy. That would explain "I have bought a card using tokens without clicking on 'use token'".
OTOH, the game you described clearly had a bug that needs to be fixed, independent of any undo requests. Do you have by any chance the game number?
No I didn't take it down. I tried leaving the table and coming back but i think it may have just continued to not even load. So I just resigned.