After a discussion with Zac on irc, we agreed that the below commit [1] is too restrictive and should be reverted from portage. [1] dd2d661078771a41d4fd554c2bc3b1188ce7b53e
Reverted: http://git.overlays.gentoo.org/gitweb/?p=proj/portage.git;a=commit;h=8dd1f89c91dac45c7db4984a93249ed494fa2323
This is fixed in 2.1.11.61 and 2.2.0_alpha172.