I started using 11.1 a few weeks ago with KDE4 and now I switched to Gnome (KDE still installed).
When a user has locked the screen and another user tries to log in by clicking "switch user", I get the following error on a popup:
Unable to start a new display
The name org.gnome.DisplayManager was not
provided by any .service files
...and the new user isn't prompted for login.