xfce4-panel and compiz

[Foxy]

As you can see on a screenshot here 
http://ubuntuforums.org/attachment.php?attachmentid=9396&d=1147469911 
the panel does not aligned to the top of the screen when used with compiz.

It happened after a recent upgrade of Ubuntu Dapper. The panel version 
is now r21633. As both compiz and xfce4-panel have been upgraded I have 
no idea what is the problem. The panel works fine with xfwm4 and compiz 
works fine with the gnome panel in Gnome.