I ended up losing a PAID first class flight because of a plane change (went from 16 FC seats to 12 due to mechanical problems where they swapped planes)- was denied boarding in first class. Yes, I paid for F. Yes, I didn't get the 1.5x BIS miles you get for FC, either (had to talk to customer service on that one). I did get an upgrade coupon for a future flight, but it's a little hazy if I can use it like an MVPG coupon (where it bumps any coach fare), or if it's one where you have to have an upgradable fare.

That might be another reason you lost your first class, too...