With desktop effects enabled when using gksu system gets grey and only responds to keyboard

[António Lima]

I have a ati graphic card with oss divers and when I activate the desktop effects in feisty, when I try to make some administrative task and have to enter my root password, after doing it my system stays with a grey color and does not responds to mouse. Also the administrative application (for ex. synaptic) apparently does not start. Doing alt+F4 closes the makes the system get back to normal but synaptic is not open (of course... I know, i closed it :)).
I have feisty up to date today (12/04/2007).