This problem was noted after switching from Metacity to xfwm4 under Fedora
Core 1 (fully updated).  There are some screen shots here (which I will
leave up for a while):

1. After a fresh login with top panel shifted downward:

http://www.medanalytics.com/Screenshot.png

2. The way it "should" look:

http://www.medanalytics.com/Screenshot-1.png

3. When I change the bottom panel to "left", it is now vertical, right in
the middle ofthe screen:

http://www.medanalytics.com/Screenshot-2.png

3. If I then click on "Expand", it then does shift to the left hand side of
the display:

http://www.medanalytics.com/Screenshot-3.png

4. If I then change the panel back to "Bottom", with no "Expand", it is
horizontal in the middle of the screen:

http://www.medanalytics.com/Screenshot-4.png

5. Finally, if I now "Expand", it shifts to the bottom , but "leftjustified":

http://www.medanalytics.com/Screenshot-5.png

I cannot get it to return to the bottom and centered, even after a full
re-boot. However, after a clean re-boot, note where the panels are now.
That is the bottom panel on top of the top panel, which is shifted downward:

http://www.medanalytics.com/Screenshot-6.png

I am quoting Olivier Fourdan from XFCE here, as it was he who spent the
time to track this one down. Note that Olivier used the Gnome, not the
Fedora Core, sources on this to replicate the problem on his system.

"The GNOME panel from GNOME 2.4 doesn't set the ICCCM standard
flagPPosition so the panel are not placed correctly. Metacity doesn't show
the problem as it doesn't place windows of type DOCK, SPLASHSCREEN,
etc.anyway, so they get placed correctly anyway, but that's no standard.
The standard is to use PPosition."

"The problem shows in xfwm4, kwin and plenty of other window managers"