Comment 4 for bug 508752

Reopening the report: The problem occurs on my system as well.
I am running a Dell Latitude E4300 with an external monitor connected. The integrated intel VGA chipset is used with the xserver-xorg-video-intel_2.9.1-3ubuntu5 driver.
The dual screen is set in panning mode with the following command:
    xrandr --output VGA1 --mode 1600x1200 --pos 0x0 --output LVDS1 --mode 1280x800 --pos 0x0 --panning 1600x1200//100/100/100/100
The effect is as described in the update of the bug description:
The mouse works nice and smooth except in the moment when the smaller screen pans. At that time, the mouse is observed to move erratically on the larger screen, jumping back and forth by perhaps 20 pixels.
I have yet to try whether the "nomodeset" kernel option fixes the problem.