The almost absurd obsession with getting things just right often displayed by Polytron founder Phil Fish is well known among most independent gaming circles, especially now that said obsession has been shown to the world at large via Fish's role in Indie Game: The Movie. Having seen the anger and anxiety Phil shows when things don't go quite right, it's not too terribly difficult for one to imagine how he might be reacting to the realization that the first patch for Fez is kind of broken.
Yes, Polytron's long-awaited patch to its previously long-awaited Xbox Live Arcade game has arrived, and it does fix many of the issues intended, including several crash bugs and save file issues. However, it also comes with a very important caveat, in that it may now read your save file as corrupted. The good news is that there is a potential workaround. If you flush your Xbox 360 cache, it should fix the problem. However, if it doesn't, then there is currently no other solution. It's worth noting that flushing your system cache deletes all patches and updates to the system, which means that the game will just ask you to install the patch again upon reboot. You'll then have to play the game offline to avoid installing the patch.
Polytron, for its part, is "floored" that the issue wasn't discovered during testing, and will update on the situation once they know more.
So, hey, maybe don't install that patch just yet. And if you see Phil Fish walking around cursing up a storm, maybe give him a little breathing room until all of this is resolved. There's no sense in upsetting him more than he almost assuredly already is.