So, I tried to save and share a tune for the Ferrari F50 and then my game crashed. Now, every time I create a tune for that car (without sharing it), it becomes corrupted and I cannot load it. My game still crashes if I save and share a tune.
https://forums.forza.net/turn10_postst123198_build-and-tunes-will-save-but-then-forza-wont-recognize-them.aspx
https://forums.forza.net/turn10_postst123108_2012-Nissan-GT-R-Black-Edition---Bug.aspx
Only the one car it does it for on mine, but it persists after a hard restart, a night in bed, everything.