+++ This bug was initially created as a clone of Bug #85280 +++ Given that there is no intention of fixing Bug #85280, how about making the very small effort of updating the manpage of newgrp and gpasswd to explain that they were not updated for PAM and that using a password to change group is not going to work. I would expect that every time a bug is set to "CLOSED WONTFIX" there should be a corresponding manpage update.
In FC4 it should be fixed by newgrp from shadow-utils and for FC3 I have a patch that will be available in a next util-linux update.
Fixed in FC3 update util-linux-2.12a-24.3.