There were many bugs in the threading code of older versions of perl, which have generally been fixed now. So I would recommend you try it with the newest version of perl you can (e.g. 5.14.2) and see if the problem goes away.

What version of perl are you using, and on what platform?

Alternatively, if you use any modules that use XS rather than being pure perl, then the bug may reside in that module. Try if possible to reduce your problem to the smallest complete program that has as few external dependencies as possible.

Dave.