I've had a similar thing happen to me too. A character that I was working on suddenly had her head disappear (and no, the head was marked as being visible). All that was left was a pair of eyeballs!? Whilst completely unexpected, and somewhat frustrating, it did give me some ideas for some other interesting picture creations. Fortunately I had progressive saves of the character and could go back to these, but it does seem to be the case, even with the 4.03 patch, that frequent saving is the best idea.