Is there a known issue with 8800GTX cards and the flat-panel display
fixed-aspect ratio option?

On my partner's system it is impossible to select the Nvidia Control Panel's
flat-panel display fixed-aspect ratio scaling option. The moment you hit
Apply it reverts to "Use my display's built-in scaling". This means games
or apps that naturally run at, say, 1280x1024, are distorted as they are
stretched to fit the display. On my system with the same monitor driver,
same video driver, etc, it works perfectly. The only relevant difference as
far as I can see is the video card.

My partner's system:

XFX o'c 8800GTX
163.75 driver (fixed aspect ratio option does not work)
Samsung 215TW monitor (1680x1050) DVI connection

My system:

XFX o'c 8600GTS (my XFX o'c 7800GT died under waranty)
163.75 driver (fixed aspect ratio option works)
Samsung 215TW monitor (1680x1050) DVI connection