Re: [BUG] Kubuntu-AMD64-NVidia driver
Ok... problem solved (well, not really but it is at least, diagnosed).
The (K)Ubuntu splash screen with its progress bar is conflicting with the nvidia driver for some reason leading to the strange X11 behavior described.
Solution for now, turn off the (K)Ubuntu splash screen, by doing:
sudo nano /boot/grub/menu.lst
and then editing any kernel line of the form:
kernel /boot/vmlinuz-2.6.17-10-generic root=/dev/sda1 ro quiet splash
kernel /boot/vmlinuz-2.6.17-10-generic root=/dev/sda1 ro quiet
(ie. removing the splash screen)