Comment 4 for bug 227520

After various changes in my xorg.conf for other reasons (dri, compiz etc. ) I decided to try the dual monitor issue again and I realized that I can't reproduce the both-sides-cropped display on the external monitor anymore.

With the laptop display off I could also change the resolution of the external monitor normally:

e.g. using
xrandr --output LVDS --off --output VGA-0 --mode 800x600
xrandr --output LVDS --off --output VGA-0 --mode 1024x800

changed the appearance of my display reasonably.

Having the laptop display on instead, it wasn't possible to change the external monitor's resolution:

running
xrandr --output LVDS --mode 1280x800 --output VGA-0 --mode 800x600 (A)
or
xrandr --output LVDS --mode 1280x800 --output VGA-0 --mode 1024x768 (B)
has no impact on the appearance of the external monitor (it seemed like it was stuck to 1024x768, although the star symbol in the xrandr -q output changed place correctly)

for both (A) and (B) I could see on the external monitor the lower right portion of my desktop surface (I suppose 1024 from 1280 in width direction and 768 from 800 in height direction).

The cropped/distorted stripes on left and right side of the display (like with not supported monitor resolution), described in my first post, don't occur anymore.

Anyway I am happy that I can connect an external projector (to make a presentation for example) without restarting the Xserver even if I have to turn off the LCD display.