Aloha Snap,
Curiously I can get my Cadimage Door and Window Builder windows to opaque what is behind the windows by selecting a material that does not have transparent properties. In my case this is a material called Glass Blue instead of using Glass Clear.
Because I have not figured out how to control the 2D transparency of the ArchiCAD windows I'll use the windows that I create using Cadimage's Door and Window Builder. Besides that the Cadimage Door and Window tools seem to be much easier to use and work much better resident ArchiCAD Door and Window tools.
Aloha,
John