* DEFINED OVERLAYS DON'T EXIST! This probably happens with other versions too. I was able to work around (fix?) this issue by editing line 297 of /usr/bin/g-cpan. unless (keys %{$gcpan_run->{portage_bases}} > 1) becomes unless (keys %{$gcpan_run->{portage_bases}} >= 1) and g-cpan won't exit early when you only have one overlay defined in PORTDIR_OVERLAY.
fixed in svn. sorry about that, seeing this makes it feel even sillier to have missed earlier.