We've made a few small updates to perl-cleaner that should get you around subslot issues much better in the future.
If you are planning to do any major Perl update on your Gentoo box in the near future, please as a first step update to =app-admin/perl-cleaner-2.14, which is currently in ~arch but in my opinion a good stabilization candidate. This will hopefully give you a much better upgrade of your Perl modules.
Of course any feedback is appreciated, and if you encounter problems, please file bugs! If nothing unexpected happens, =app-admin/perl-cleaner-2.14 will go stable in a month.