If that aids debugging, command "LANG=C sudo adduser test28" fails with:
Adding user `test28' ...
Adding new group `test28' (1004) ...
Adding new user `test28' (1001) with group `test28' ...
useradd: cannot lock /etc/passwd; try again later.
adduser: `/usr/sbin/useradd -d /home/test28 -g test28 -s /bin/bash -u 1001 test28' returned error code 1. Exiting.
So this is probably the same issue as bug #432964, but I still think gnome shouldn't show the new user in the GUI but instead show an error message.
If that aids debugging, command "LANG=C sudo adduser test28" fails with:
Adding user `test28' ...
Adding new group `test28' (1004) ...
Adding new user `test28' (1001) with group `test28' ...
useradd: cannot lock /etc/passwd; try again later.
adduser: `/usr/sbin/useradd -d /home/test28 -g test28 -s /bin/bash -u 1001 test28' returned error code 1. Exiting.
So this is probably the same issue as bug #432964, but I still think gnome shouldn't show the new user in the GUI but instead show an error message.