Polytron calls the update "kinda broken."
Indie darling Fez now has a major title update (aka patch) out on XBLA that adds some performance improvements, fixes some crashes and glitches, and even corrects some errors in the French localization. You know, all the things patches are supposed to do. What patches aren't supposed to do, however, is corrupt your save files.
"THE PATCH IS KINDA BROKEN," wrote a message on the Polytron Twitter account. "Reports of savefile corruption. We advise against installing it unless you already can't play the game."
An update on the Polytron website further clarified the situation. "There is an issue that seems fairly widespread where the save file can be seen as corrupted by the game after installing the patch. We're floored that this wasn't found in testing."
For the moment, users who encounter this problem can delete their system cache, which should resolve the issue. If that doesn't work, though, there isn't another workaround.
Polytron says it will keep everybody updated on the situation.