Comment 5 for bug 488099

Here's an excerpt from my ~/.xsession-errors file that is probably relevant.

Exception in Gtk# callback delegate
  Note: Applications can use GLib.ExceptionManager.UnhandledException to handle the exception.
System.NullReferenceException: Object reference not set to an instance of an object
  at Do.Interface.PositionWindow.GetMonitor () [0x00000]
  at Do.Interface.PositionWindow+<UpdatePosition>c__AnonStorey3.<>m__8 (System.Object , System.EventArgs ) [0x00000]
  at Gtk.Application+InvokeCB.Invoke () [0x00000]
  at GLib.Timeout+TimeoutProxy.Handler () [0x00000]
   at GLib.ExceptionManager.RaiseUnhandledException(System.Exception e, Boolean is_terminal)
   at GLib.Timeout+TimeoutProxy.Handler()
   at Gtk.Application.gtk_main()
   at Gtk.Application.Run()
   at Do.Do.Main(System.String[] args)