Currently the suffix txz is not recognized as tar.xz >> Unpacking beast-mcmc-1.7.5.txz to /var/tmp/portage/sci-biology/beast-mcmc-1.7.5/work unpack beast-mcmc-1.7.5.txz: file format not recognized. Ignoring. Should be simple to fix
PMS doesn't mention the txz extension yet: http://dev.gentoo.org/~ulm/pms/5/pms.html#TBL-42
In EAPI 6: https://gitweb.gentoo.org/proj/pms.git/commit/?id=a16308ff92bdc7bb6cf2e672873b5ab0d7190e4c