Blank screen on second login if user has Compiz enabled

[Johannes Dahl]

In my Intrepid Ibex system, in a situation where user A is logged in, user B is unable to use the system if user B has Visual Effects enabled (it doesn't matter whether user A does). It is possible for user B to log in, but the display remains pure white with the only visible thing being the cursor on it. It is possible to e.g. run a browser and resize it using feedback from the cursor to locate the edge of the browser, but that's not much of a use. Pressing ctrl+alt+backspace has the effect of showing the wallpaper and placeholders for panels for a split second, then logs out.

If it is relevant, my computer has an Ati Radeon 9800pro video card and I am not using the proprietary drivers.

Thanks for your time.