The edid from your panel has bad size data:
(II) RADEON(0): clock: 71.2 MHz   Image Size:  289 x 21 mm
It looks like they specified the height in cm rather than mm. IIRC, newer xservers (git master maybe) have a quirk to deal with these kind of problems, but I don't know if the patch is in xserver 1.5.x.  You can override it in your xorg.conf.  See the "Changing DPI and DisplaySize" section of this page:
http://wiki.debian.org/XStrikeForce/HowToRandR12

On Fri, Nov 14, 2008 at 09:34:19 -0800, bugzilla-daemon@freedesktop.org wrote:

> (II) RADEON(0): Max Image Size [cm]: horiz.: 33  vert.: 21
> 
> (II) RADEON(0): clock: 71.2 MHz   Image Size:  289 x 21 mm
> 
> (II) RADEON(0): Setting screen physical size to 289 x 21
> 
> 
> The 21 mm size does crazy things.
> 
the server already has a quirk that should apply to your monitor and fix
this, but somehow it's not used?

static Bool quirk_detailed_use_maximum_size (int scrnIndex, xf86MonPtr DDC)
{
    /* Bug #10304: LGPhilipsLCD LP154W01-A5 */
    if (memcmp (DDC->vendor.name, "LPL", 4) == 0 &&
        (DDC->vendor.prod_id == 0 || DDC->vendor.prod_id == 0x2a00))
        return TRUE;

    return FALSE;
}

Does seem to be activated:
(II) RADEON(0): EDID vendor "LPL", prod id 0
(II) RADEON(0):     EDID quirk: Detailed timings give sizes in cm.

But it's really only the vertical size that is reported in cm, or is just plain wrong:

(II) RADEON(0): clock: 71.2 MHz   Image Size:  289 x 21 mm

Certainly don't want to multiply both by 10:

        if (quirks & DDC_QUIRK_DETAILED_USE_MAXIMUM_SIZE) {
            det_mon->section.d_timings.h_size = 10 * DDC->features.hsize;
            det_mon->section.d_timings.v_size = 10 * DDC->features.vsize;
        }

> --- Comment #3 from Orion Poplawski <orion@cora.nwra.com>  2008-11-14 10:29:18 PST ---
> Certainly don't want to multiply both by 10:
> 
>         if (quirks & DDC_QUIRK_DETAILED_USE_MAXIMUM_SIZE) {
>             det_mon->section.d_timings.h_size = 10 * DDC->features.hsize;
>             det_mon->section.d_timings.v_size = 10 * DDC->features.vsize;
>         }
> 
DDC->features.{h,v}size are the dimensions reported in:

(II) RADEON(0): Max Image Size [cm]: horiz.: 33  vert.: 21

They are in cm, so multiplying them by 10 is correct.