Using the Arch window tool when a window is selected now produces

a clone

src/Mod/Arch/ArchWindow.py

@@ -33,6 +33,10 @@ __url__ = "http://free-cad.sourceforge.net"
 def makeWindow(baseobj=None,name="Window"):
     '''makeWindow(obj,[name]): creates a window based on the
     given object'''
+    if baseobj:
+        if Draft.getType(baseobj) == "Window":
+            obj = Draft.clone(baseobj)
+            return obj
     obj = FreeCAD.ActiveDocument.addObject("Part::FeaturePython",name)
     _Window(obj)
     _ViewProviderWindow(obj.ViewObject)

src/Mod/Draft/Draft.py

@@ -1581,8 +1581,11 @@ def clone(obj,delta=None):
     if not isinstance(obj,list):
         obj = [obj]
     cl = FreeCAD.ActiveDocument.addObject("Part::FeaturePython","Clone")
+    cl.Label = "Clone of " + obj[0].Label
     _Clone(cl)
-    _ViewProviderDraftPart(cl.ViewObject)
+    if gui:
+        _ViewProviderDraftPart(cl.ViewObject)
+        formatObject(cl,obj[0])
     cl.Objects = obj
     if delta:
         cl.Placement.move(delta)
@@ -2813,3 +2816,6 @@ class _ViewProviderDraftPart(_ViewProviderDraft):
     def getIcon(self):
         return ":/icons/Tree_Part.svg"
 
+    def claimChildren(self):
+        return []
+