SigSegV during stack unwind (AIX)

Hi
I am getting a strange segmentation fault during the unwind
process. I am trying to throw an object of an Exception class.
During the DoThrow (in libC.a) the stack starts growing until a
Signal is received.
The object thrown is of a class that inherits from a common class,
and the signal only appears rarely - but consistently when it does appear.

I am useing xlC V8 on Aix 5.3 . Dod anyone experience/heard of something like this ? Could it be a copiler problem ?

Thanks