In my recent bout of distro hopping from Elementary Freya to Deepin 2014.1 and now to Ubuntu Utopic Unicorn. I found that I had a problem with the login screen down on b both my monitors. My preference is to have it only showing on my external monitor. I Didn’t have this problem admittedly under Deepin so it was frustrating under Ubuntu.
The solution is to do the following.
1) login to the system
2) use the display utility to configure the screen to show the external monitor only. This also solves another problem of Nvidia not remembering the display settings.
3) open a terminal and run the following command
sudo cp ~/.config/monitors.xml /var/lib/lightdm/.config
4) reboot and login. The login screen should now be only showing on one monitor.