I was just spectating this game...
It took me a minute to understand what the problem was, but obviously you shouldn't get the buttons to Grant/Deny the request.
I basically never spectate, could any regular spectators tell me what the usual behavior is for a spectator when an undo request is made? Is the "Request to undo" box shown, or does it come as a surprise when the game suddenly rewinds?
The usual behavior is to not be shown the undo request.
I've seen those as spectator quite often, but I think not always. Haven't been able to detect any pattern, unfortunately.