see summary Reproducible: Always
And that's a good thing, IMHO.
This is fixed in git: http://git.overlays.gentoo.org/gitweb/?p=proj/portage.git;a=commit;h=c86c05e07c5060d1a81b8b8a3880175260d79a45
This is fixed in 2.1.11.61 and 2.2.0_alpha172.