I see what you mean now, I think. I don't have a good model of dealing with a situation where someone can influence the actual updating process either. I was always thinking of a setup where the sorcerer affects something other than this.

By the way, I remember reading a book which had a game-theoretical analysis of games where one side had god-like powers (omniscience, etc), but I don't remember what it was called. Does anyone reading this by any chance know which book I mean?