When I first started playing and I didn't know about the "/undo" or "/undo x" commands, I thought the undo couldn't undo bot commands. I later realized it was undoing a single bot move, but then the bot was almost instantly repeating what they did before. This behavior isn't very useful in my opinion.
There are no situations where I've wanted to undo a bot's move just to let him repeat it again (unless I'm hoping they aren't deterministic and would change their decision? I've never tried this though), and there are plenty of situations where I wanted to undo my last move (say a militia discard I screwed up) and it'd be nice if the undo went back to my last decision. Having to type /undo, scroll down the log (because the log automatically scrolls to the top) finding my move and clicking it seems a lot harder than what I believe should just be the default behavior.
This would make the behavior a disconnect between bot and human games. It wouldn't be a terrible default behavior for human games, but I could see someone undoing for a friend they are teaching or something like that. Mostly I just want it for bot games because even if you hit undo right away the bot could've easily taken several moves in that time.
I would extend this to games with human opponents. Undo shouod always undo my last move. Why would I want to undo an opponent's move?