Comment 104 for bug 969489

I got better result using default lightdm greeter instead of ubuntu's one. Maybe this can help others.
sudo apt-get purge lightdm
sudo apt-get install ubuntu-desktop
sudo apt-get install lightdm-gtk-greeter
If lightdm-gtk-greeter is installed, you will not be able to start neither ubuntu-greeter, nor default gtk greeter. After the installation of the gtk-greeter, ligthdm will default to this one.