Comment 2 for bug 726892

In fact, I was wrong. When using xrandr to switch to external screen, it is not wrong resolution, but the screen is split in half again only this time the upper part shows no garbage - only black background. The picture of the desktop is shown only in the lower left part of the screen is 1024x768 and it works OK without problems.

The mouse is able to move to the black parts on the top and right.