Bug#488277: I have exactly the same problem
First thanks for your help.
I removed the mode lines from the screen sections. I did not add them
back to the monitor section as they are correctly probed by the driver.
The modes in your screen section apply to all outputs. The ones in
your monitor sections only apply to the specific monitor in question.
Result is no change. The display on the external lcd is only a portion
of the whole 1400x1050 resolution. Explicitly setting the resolution of
the LCD, does not change anything. I still have to resort to the script
docked to have a correct display.
If you have any other suggestion, please tell me I will give it a try.
NB: I would prefer to have a single configuration file for both config.
Using xrandr or a script like today is ok. With kde4, krandrtray will
enable to to this graphically.