This is the only ebuild, which were not rebuilt against Perl 5.8.7, so I emerged it by hand, later. The install went fine and the files in /usr/lib/perl5/5.8.6/ were removed as well afterwards, so I'm a bit clueless why perl-cleaner didn't catch it. It's not even listed in the log file.
At one point Class-MethodMaker wasn't installing in the right place, which might have confused perl-cleaner as to whether it was a package it should be governing or not. Afraid I can't dup this and without a perl-cleaner log couldn't begin to confirm that suspicion. Afraid I have to close this as can'tfix for now :/
I can attach the log, if it helps you to find out what happened. Just that it's not referencing Class-MethodMaker. Drop a line if interested, otherwise ignore the spam. ;)