Perl 5.8.5 is really old. It is not even the latest in the 5.8 series. Consider using at least 5.8.9 (the last in the 5.8 series), or consider using a supported version of Perl, like 5.14 or 5.16.

If you are compiling Perl from source and yet cannot change the 5.8.5 version, I recommend looking through the changes to pp_sys.c after 5.8.5. Maybe that bug was fixed for HPUX. The blame log for pp_sys.c may or may not help there.