I find it really odd that

perldoc -f use reports that all is like it should be

I could be wrong, but I thought use came in with Perl 5. I do know perldoc first appeared in 1995, which is about the same time as Perl 5.001.

Are you sure you don't already have two versions of Perl installed? I haven't worked on HP-UX in a while, but it used to come with both Perl 5 and Perl 4. In the systems I was on, /usr/bin/perl was Perl 4, and /users/contrib/bin/perl was Perl 5. Try looking around your system awhile.

Sorry if this is all so obvious that you've already tried it. If you have, then follow merlyn's advice above. ;-)