I don't have anything resembling a solution, but I dimly remember having digged around in the same piece of code, while trying to come up with an explanation for another somewhat related problem  (though that was Net::SSLeay in combination with PAR::Packer — so read down a bit in the thread).  Unfortunately, as far as I can tell, the problem never got resolved... but maybe you'll find some additional pieces for the puzzle (if you haven't come across that thread already).  At least, it seems to confirm that - under some circumstances - something strange is happening with the errno values...  Good luck anyway!