This is mentioned as fixed in just about every release thread, and likewise someone else always discovers a new battery drain that wasn't there before, it's honestly quite funny. My guess is that it's never (except for that one time where the WiFi never shut off or something) actually fixed or caused by any update, but that it's always related to outside conditions that coincidentally changed around the time of the update (phone masts being replaced, a rise or drop in temperature, and so on). I can't think of any other way to explain the phenomenon.