Just came back to WoW. 2.3 lured me back in damn it :D I was getting the message in chat about an addon tainting the UI, so I enabled the log. Three addons showed up, DoubleWide, NQuestLog, and TourGuide. The tainting from all three addons was usually related to QuestWatchFrame:Hide. Just wondering if this is a Blizz bug or what exactly?
Addons that interact with the watcher taint it, and in turn taint the panel positioning code. I've seen no ill effects from this, but I do believe that Blizzy is replacing the positioning code to get rid of this issue.