The probably reason why a few people know and so utilize it. Reproducible: Always Steps to Reproduce:
Btw, what does it do?
Hard to explain in *words*. Just add it and emerge -pv portage or in that case any package.
Thanks, this is fixed in git: http://git.overlays.gentoo.org/gitweb/?p=proj/portage.git;a=commit;h=b945d359b14c1f2590fbbcbf8f8689c60f188e8b
This is fixed in 2.1.9.2 and 2.2_rc78.