I had a similar event with my SU-22. Brass went over the top and was banging around behind the bolt. The spent brass was banged up pretty well by the time I got it out of there. The firing pin broke around that time and that may have been related to the brass falling between the hammer and the firing pin.
 
Firearms can be dangerous when operated that far from their intended operation, and I'd never intentionally do that, but the SU-22 functioned surprisingly well. It ejected well, and even with the firing pin in two pieces, it'd operate properly on all but the first round out of the magazine. With the front half of the broken firing pin hanging out the front of the bolt, the first round out of the magazine would jam onto the firing pin and not feed up onto the bolt face, forcing me to gingerly feed the first round. Afterward, it'd feed just fine!
 
Allowing brass to flip over the top of the bolt and land behind it may be an artifact of using the PLR-16 receiver when making the PLR-22.
 
I've shot many thousands of rounds in my SU-22, and this has only happened once to me, so it's not a common problem.

Quote from ktwm on 04/09/10 at 15:22:56:

 
Serial # Starts "UOE"...

sorry. my post should have gone to su22, not plr22