Unable to choose primary monitor

[Håkon Enger]

After upgrading to 16.04, I am unable to choose the right monitor as "primary" using Unity. Before, I could select the primary monitor using, e.g., "xrandr --output DP-1 --primary", but now it seems that "something" is reverting this setting immediately, resulting in screen flickering for a few seconds and afterwards the left monitor is the primary again.

I have also tried to edit the file ".config/monitors.xml" and change the <primary> tag content to "no" for the left and "yes" for the right screen, but this results in (after running the xrandr command) a black screen with some flickering for a while before Xorg finally crashes, and I am unable to log in (same black screen with flickering and X crashing) until I edit the file to have the primary monitor on the left again.

I am using nvidia drivers (currently 370.23, also experienced the same problem with 367.35 and 364.19), but I am not sure if that is relevant.