Screensaver not saving screen

On my widescreen laptop, “Euphoria” screensaver SOMETIMES covers the whole screen, and sometimes cover about a quarter…looks like about 640x480 (on a 1440x900 screen). The rest of the screen is white.

I’m using 11.0, with KDE4.1, but if I recall, I had this problem under 10.2 and KDE3.5 also, using any openGL screensaver. The laptop is an HP dv9205us; it has an nVidia card (GeForce 6150).

Has anyone had the same problem, and fixed it? I’ve googled to no avail. Thanks in advance,