Comment 9 for bug 394691

It happens on nividias (tested afair something like 5200fx, 7200? and gts 220?), it also happens on intels (various i945-like).

To trigger it:
1. Wait until screen saver starts (the default black one)
2. Move mouse, you will see that the black rectangle covers only PART of the screen (from 0,0 top-left, to some other point)

This happens sometimes, it seems that it helps if:
1. you are using few VTs, like VT-7, VT-9 - login as second desktop user at same time (switch user)
2. you are changing video resolutions (start some fullscreen program, best a 3d game and switch resolutions a bit)
3. it also helps a lot if you use 2 outputs like LVDS + VGA on linux (then, on intell, it happens very often).

If it doesnt happen then try again later.
It happens around 1 per few days of using (switching desktops/resolutions few times a day)
It happens more often afair on the dual headed laptops (2 displays different resolution)

In either way, there should be some naive code like I written previously, with rectangle drawing or something right?
So just change it to always draw a HUGE rectangle, because the problem apparently is because screen saver has the wrong (old, smaller) dimensions of the screen remembered!

Just make it draw huge rect and done.

Or better, why is so naive implementation used, there should be something dedicated in X server, like stoping rendering of all other windows or something (in example, the clock keeps running / refreshing if it "sticks out" from the too-small black rectangle of screensaver. Why it refreshes at all?!)