Set a.ConnectedBaseWorkingOverlay = b this works.

Just close and open the WL once if does not show correct result.

I think, you need an automated refresh of the wl in the user interface. 

' let a be the other workinglayer
If Workset.Globals.Exist("AppCommand") Then
   SetAppCmd=Workset.Globals.AppCommand
   If NotAppCmd Is Nothing Then 
      AppCmd.Execute"ReOpenProjectByWO",a
   End If 
End If

Hope this helps you.

Guido