When using the menu from the desktop, all xfce-settings-show actions seems to fail silently, nothing happens. However, the same action performed from menu on the panel works fine... This is with gtk+-2.11.x - Odd heh? Thing is they changed the way gtk selects PropertyNotify events (ie, it doesn't select PropertyNotifyMask anymore), see this bug in Gnome: http://bugzilla.gnome.org/show_bug.cgi?id=354213 Maybe it's related? Dunno.
Actually, the menu doesn't spawn any application at all (not just settings) when used from the menu...
Ok, found out what happens here... Seems gtk+-2.11.x now expects the same button to be pressed as the one given by gtk_menu_popup() to activate the menu entry or it does not activate the entry at all. In xfdesktop, the menu is opened with the right mouse button, so gtk+ was expecting the right mouse button to activate, and was discarding the usual left mouse button. To fix this, use mouse button 0 in gtk_menu_popup() and all is fine again. The fix has been committed in xfce_4_4 and xfce_4_2 branches.
Created attachment 1273 lways use button 0 in gtk_menu_popup() as GTK+ 2.11+ expects the same button to be pressed or it doesn't activate the entry Patch added for the record.