dev-perl/IO-Multiplex is licensed "under the same terms as Perl itself". Perl has been "|| ( GPL-1 GPL-2 GPL-3 Artistic )" since at least 2006, which is before IO::Multiplex was released under these terms.
cvs/gentoo-x86/dev-perl/IO-Multiplex $ ebuildvar LICENSE IO-Multiplex-1.09.ebuild : LICENSE="Artistic" IO-Multiplex-1.130.0.ebuild : LICENSE="|| ( Artistic GPL-1 GPL-2 GPL-3 )" This is entirely correct, since IO-Multiplex-1.09/work/IO-Multiplex-1.09/lib/IO/Multiplex.pm points out it is released under the Artistic license. For the newer version, the license terms changed and the ebuild properly reflects that.