The panel autohide feature works after panel is started. Later, it stops working and the panel is stuck open. This is unpredictable but I believe it usually occurs after using the XFCE Menu (the applications menu) - not every time I use the menu, but eventually. Running xfce4-panel in a terminal, the only message I get from the panel is: ** (xfce4-menu-plugin:16425): CRITICAL **: Unable to get keyboard/mouse grab. I can post any logs or config files that could be useful, just tell me what they are. This is in Ubuntu 9.04 with XFCE 4.6.0, but I also experienced the same bug with older versions of Ubuntu & XFCE.
Looks like a bug in xfdesktop. @ Brian, this is probably caused when gtk_menu_popup fails, and thus deactivate is never called. I think you can work around this by checking if the menu has the grab after gtk_menu_popup (this is the last thing set in a successful gtk_menu_popup). See patch attached.
Created attachment 2581 Only register menu if it is grabbed.
This bug is also extant in XFCE 4.6.1 (I'm also seeing it on a shiny new Xubuntu 9.10, amd64).
checked in on xfce-4.6 and master