The block to speak to will be wrxhoon. He knows his stuff, and I belkieve what he says.
Sydneykid on the otherhand does not beleive it can happen. Many other people have experienced this. I believe gtr geoff did too?
I can't remember the exacts of it, but basically, it's the ceramic exhaust wheel. What happens, is it hits the turbo housing, and breaks into little pieces forming dust. due to the valve timing, at certain times, the engine is under vaccum - keep in mind there are only 3 cylinders. it is much less likely to happen in a gtst with all 6 poushing gas continuously through the exhaust.
basicall,y it's not going to kill your motor straight away. it's not like it won't start. what it does do is scratch the cylinder and the piston. wrxhoon still has the pistons he removed from the engine after the stock turbo blew.
My suggestion would be to definitely don't drive it. dump the engine oil through coffee filter paper. if you feel grittiness in there, then I would imagine it would be rebuild time.