1680x1050 extends beyond physical screen limits / wrong hsync?

[Stefan Dietrich]

h/w: acer travelmate 382tmi, intel855gm gfx, lg l226wtq-sf 22" tft
s/w: xubuntu 7.04, xorg 1.3.0, xorg-xserver-video-intel 2.0.0, xrandr
1.2

my external 22" tft is connected to my notebook via vga, if i manage to
set it to the native resolution (1680x1050), the image is "stretched" by
approx. 30..40%, thus extending beyond the physical screen limits and
disappearing in those parts. due to the stretching, fonts appear a bit
distorted. horizontal scrolling to the invisible part is not possible.
at lower resolutions the image fits fine. my tft only supports adjusting
image position, not changing the size.

i read about this issue with the same resolution and different video
drivers, too. some of these could be fixed by using different modelines
or metamodes (1680x1050_60). i tried some of these, but without success.
however i'm not sure if i did all modifications correctly.

some people claimed this problem is due to wrong horizontal sync, i can
to some extent confirm this: if i adjust the hsync via the tfts osd,
that is, lowering it from 64 or sth. to the very minimum (which is in
fact zero but this lacks plausibility), the display width shrinks a bit,
but only for about 30..50 pixels.

any suggestions where to start?
if you want any xorg.conf oder Xorg.0.log output, please let me know.


thanks in advance,
cheers,
Stefan