After doing some digging, I think the whole thing is a misnaming issue on the part of Gurusamy. According to the CPAN module, if you put an underscore in the version numbering of the file, it gets treated as an unstable version and will be disregarded when checking for up-to-date versions.

I e-mailed gsar about it, and I'll see what he says. That CPAN documentation may be out of date.

Interesting little tidbit from gsar's README on CPAN:

Anything that doesn't figure in the list above is either
not related to Perl, or hysterical junk that you should
probably ignore.
[download]

perl-5.6.1-TRIAL1.tar.gz isn't listed in his list (last updated 17-DEC-2000). Go figure.