Just installed Ubuntu 16.04. It uses lightdm and unity-greeter.
If only one user is logged in (Unity session), the login screen does not look fine after logout, these indicators are missing: power, sound, keyboard …
Is it a bug ?
The only thing there is in the top right corner is 'onscreen keyboard' menu.
In a console (ctrl-alt-F1), restarting lightdm brings the indicators back.
After a machine reboot on the other hand, the login screen has everything.
The bug has been confirmed, in this Launchpad tracker. There is a fix committed to the lightdm package, version 1.18.2-0ubuntu2.
It's currently in the proposed repo for Xenial (16.04) - I've enabled the proposed repo from the instructions here and installed the updated version. (I also followed the selective upgrades instructions, so that only packages I choose update to the proposed versions.)
If you don't want to play around with the proposed repository, that's OK - the updated package should make its way into the normal updates soon enough.
