Hey Science Boy... Good Call
I did the test and the results are below.
All of the buses where placed first before loading the window glass.
In the first image the front glass was placed first and the back glass was placed 2nd. As you can see the window in the back cannot be seen through the front window, however the buses behind can be seen.
The 2nd image is the same layout but looking the other way, The rear window was placed 1st and the front window was placed 2nd. Unlike the other view, Here you can see the frame of the rear window, and the buses behind.
I tried placing the glass 1st and then the buses but regardless of the direction, the buses were always visible through the windows.
Does this mean that the issue is with the placement order of the glass windows and how they effect each other, but other entities react correctly? I tried it with a character and another building with the same results???
Something that needs to be considered when using multiple windows which may react with one another.
There is no Spoon...