Why isn't PerlSetEnv working for me?

[Keith G. Murphy]

I'm running Apache 1.3.9 with mod_perl embedded, on Debian GNU/Linux.

I have the following lines towards the end of my httpd.conf:

PerlSetEnv PERL5LIB /usr/local/MyPerl/lib
PerlRequire startup.pl
Include perllocs.conf

However, upon system startup, my startup.pl fails because it can't find
a particular module in the @INC list.

If I start Apache from the command line, it works.  This is undoubtedly
because PERL5LIB is set up in my /etc/profile, to the same path.

I've looked at this until I'm crosseyed.  Seemingly PerlSetEnv just
doesn't work.

Any ideas?  Yes, I know the workaround: 'use lib' in startup.pl.  But
why?