As is mentioned above, I believe this is an issue with some versions of the CPAN module that shipped with earlier perls. If you upgrade CPAN, I think you'll find that it doesn't try to force you into a full perl upgrade.

When you go to upgrade your CPAN module, you can't do it from the CPAN shell because it will send you down the same rabbit hole--during the CPAN upgrade of itself, it will try to upgrade perl.

If you run the CPAN upgrade the old fashioned way (make, make test, make install), you should then be able to use the shell as before and not have it upgrade perl. The most recent CPAN will look at the newest version of a module and if it requires a newer perl, it will just bark and say it won't install without force. This is much nicer.