Hi there!
I’ve installed the Ubuntu Mate 16.04 Beta and I think I am observing a bug in the login screen:
Often shortly after the login screen has loaded, the screen flickers and if I am already entering the password when that happens, a few characters get lost and the password is not accepted so I have to reenter it a second time.
Has anybody else seen this problem? Is there a fix to be applied?
thanks! subscribed.
Let’s see if some dev comes up with a solution 
Can more people confirm that they are also experiencing a short screen flickering right after the login screen appears?
Yes, I can confirm I am experiencing the same issue with Mate 16.04.
The workaround #9 at https://bugs.launchpad.net/lightdm-gtk-greeter/+bug/1531224 works for me.
I have the same issue (Dell Latitude E6420). Workaround does not work for me (the mentioned file is not there).