I have switched from gnome to xfce and came across some issues with xfce
+ xmonad. One more prominent issue was that xfce4-panel checks if a
window manager is running. It does so by looking through all atoms with
XGetSelectionOwner().
However, XMonad does not set a window manager atom using
XSetSelectionOwner(). Therefore it takes some time until xfce4-panel
You're running stock 0.9.1/0.9.2, which is effectively 2 years old at this point. Upgrade to the darcs version; the correct version of your code (which also handles replacing and handoff from a currently running window manager, unlike yours) is already there.