Rotated screen fails

I got a two monitor setup, one normal in landscape and the other rotated 90 degrees into portrait mode.
After a recent update (a month ago) the rotated screen wont render correctly. I got relics left from windows, flickering and parts of the background image or splash screen is displayed on top of the windows leaving the monitor unusable.
If I change the monitor settings to normal (not rotated) it works ok but as soon I set it back to rotated it fails again.


Any suggestions?