When using the Xfce panel with Xinerama, the struts seem to be set wrong on the panels. The symptoms are as follows: - Windows get their title bars pushed to the top of the screen, above the top of the upper panel. - They cannot be moved down below this in any manner, although they can be dragged to the 2nd screen and then lowered. Moving them back to the 1st screen pushes them above the top of the panel again. This behavior first showed up around r19500.
Of course, the duplication is the other way around, but the new bug contains some more info. *** This bug has been marked as a duplicate of 1550 ***