User-Agent:       Mozilla/5.0 (X11; U; Linux i686 (x86_64); en-US; rv:1.8.1.4) Gecko/20070515 Firefox/2.0.0.4
Build Identifier: 

System Info:
Gentoo 2007.0
AMD64x2 4400+
2GB DDR Ram
nVidia 7100GS
Dual Head Display, using TwinView
Resolutions: 1280x1024 on both Heads (xdpyinfo reports 2560x1024)

Description:
When a panel is set with the following options, the panel reports to be 1280, when it should be 1279:

- Fixed Position
- Top * (Left, Mid, Right - they all have the same affect with the rest of the settings)
- Full Width

This extra pixel causes replaceable window managers, such as Compiz and Beryl, to not maximize properly, as it's detecting that it will intrude/collide on the horizon of the panel.

XFWM4 *DOES* handle this properly, but it causes problems with other WM's

After working with a Compiz developer, he's assured me it's a problem with XFWM4, and both the Gnome and KDE panels report 1279 as expected.
Original Bug @ OpenCompositing.org: http://bugs.opencompositing.org/show_bug.cgi?id=233

Screenshot: http://img461.imageshack.us/img461/4189/screen071807140233kf8.png

Reproducible: Always



Expected Results:  
It should maximize vertically