I have used the 'passwd' command a number of times to change my password for my accounts, including root. After rebooting my system, I try to log in entering my password. The system response with the login prompt again.
I think for this kind of problems the best thing to do is to ask for help on the Gentoo forums, on the Gentoo mailing lists or on the Gentoo IRC channels instead of filing a bug on Gentoo Bugzilla.
It is sad to read that you have problems with passwd. The situation seems to be a bit more complicate and requires some analysis. We can not help you efficiently via bug tracker. The bug tracker aims rather on specific problems in .ebuilds and less on individual systems. I have had very good experience on the gentoo IRC [1] with questions like this. Of course there are also forums and mailing lists [2,3]. I hope you understand, that I will close the bug here therefore and wish you good luck on one of the mentioned channels [4]. Please reopen the ticket in order to provide an indication for an specific error in an ebuild or any gentoo related product. [1] https://www.gentoo.org/get-involved/irc-channels/ [2] https://forums.gentoo.org/ [3] https://www.gentoo.org/get-involved/mailing-lists/all-lists.html [4] https://www.gentoo.org/support/