gcpan gets a little confused when generating ebuilds for modules that depend on mod_perl. In this specific case, generating an ebuild for CGI::Application::Plugin::Apache.pm results in an ebuild that depends on perl-gcpan/libapreq and perl-gcpan/mod_perl instead of the existing packages in the www-apache category. From my quick glance through the code, adding www-apache to @perl_dirs might fix the problem- I don't know about the repercussions of that, though.
*** This bug has been marked as a duplicate of 121607 ***