So, to summarize:
The way a GDL Object, such a a Window, appears in the Floor Plan Viewpoint is defined in its 2D Script. The 2D Script of Windows in the ARCHICAD default library are written in a way to allow for detailed graphical representation of Reveals.
The way a GDL Object appears in 3D Viewpoints such as sections or in 3D, is defined in its 3D Script. The 3D Script of Windows in the ARCHICAD default library is not written in a way to generate a Reveal in 3D, this is why you see this discrepancy between the 2D and 3D of Windows.
This has been the case with default ARCHICAD Windows as long as I remember. I suppose a long time ago they did not script the 3D part because it would have complicated the 3D script greatly and could have resulted in polygon-heavy Window elements (this is my guess). Then, over the years it just stayed that way.
You could make a wish for this to change.
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