private void MenuItemCallbackAutoShelveRunState(object sender, System.EventArgs e)
 {
     try
     {
         _isPaused = false; // this prevents un-pause following a manual start/stop
         if (_autoShelve.IsRunning)
         {
             _autoShelve.Stop();
         }
         else
         {
             _autoShelve.Start();
         }
     }
     catch
     {
         // swallow exceptions
     }
 }