Duplicate Materials - through another viewer

In trying to answer my own question as to what material to use if two are specified in the instance geometry in Collada 1.4.1 visual scene (please see my previous question: Duplicate Materials - what do I draw?) I noticed that at least one other author reading my DAE file into his viewer shows the same problem as I have:[attachment=2:3fc4fjgj]glc-player.jpg[/attachment:3fc4fjgj]. The roofs in black are the questionable material types here. (Please see: http://www.glc-player.net for a very good viewer of Collada files from which I produced this screen shot).
This image is remarkably similar to my much less sophisticated viewer:-[attachment=1:3fc4fjgj]IMG_0038.PNG[/attachment:3fc4fjgj]
However the Apple iMAC Collada viewer show the view I am expecting see:-[attachment=0:3fc4fjgj]mac_preview_version.png[/attachment:3fc4fjgj]

So my question is:- What does Google SketchUp, Google Earth and Apple iMac Collada viewer software know that me and at least one other developer doesn’t? I would be most grateful to anyone letting me know the answer to this riddle .

Best wishes
Gordon Pagan