Bug#488277: I have exactly the same problem

[Alex Deucher]

On Sat, Jun 28, 2008 at 8:36 AM, Eric Valette <eric.valette at free.fr> wrote:
> After updating to the new xserver on my nc6000 HP LAPTOP, the screen
> connected on the docking station that can only do 1280x1024 is forced at
> the flat panel resolution that is actually 1400x1050 meaning I see only
> part of the screen on my external LCD monitor. If I force to change the
> resolution to 1280x1024 using xrandr, it just kill the external display.
>  Restoring the initial 1400x1050 does not restore the video on the
> external dipslay. To restore it I have to call xrandr --auto and then Im
> back to 1400x1050.

Make sure you use the xrandr 1.2 interface, using the old xrandr 1.0
interface (xrandr -s) will not work correctly as it has no concept of
multiple heads.
xrandr --output VGA-0 --mode 1280x1024
or
xrandr --output LVDS --mode 1280x1024

>
> Of course, I did not change my xorg.conf at the beginning. Googling a
> little bit I have added the new Randr 1.2 option to attach a specific
> monitor to a specific video output (external LCD->VGA-0, Flat Panel to
> LDVS). They are correctly associated now, but it did not change the
> behavior.

The modes line from your config is part of the problem, the modes in
that line will get added as preferred modes to every output in the new
xserver.  Try removing the 1400x1050 mode from the modes lines in the
screens section of your config.

Alex