downgrading only the xorg-x11-server-Xorg package to 1.5.2-3.fc9 (and the xorg-x11-drv-evdev which had an explicit dependency on the 1.5.3 X server,
but _not_ the xorg-x11-drv-ati package) fixes the problem. So most probably the problem is in the core xorg-x11-server-Xorg package between the 1.5.2 and 1.5.3 version.
A short update to the comment #2:
downgrading only the xorg-x11- server- Xorg package to 1.5.2-3.fc9 (and the xorg-x11-drv-evdev which had an explicit dependency on the 1.5.3 X server, server- Xorg package between the 1.5.2 and 1.5.3 version.
but _not_ the xorg-x11-drv-ati package) fixes the problem. So most probably the problem is in the core xorg-x11-