This seems to be some (compile-time) configuration option, as none of my perls exhibit that behavior. I've tried with various versions from 5.8.4 to 5.10.0, self-built and/or those that ship with Debian and SUSE Linux. All do produce identical results for PERL5LIB and use lib (both existing and non-existing dirs).
As you're getting directories for all kinds of versions, I guess it's the configure option that's scanning for other installations of Perl... (which I never use, as I explicitly do want to keep my versions separate).