Raytrace Render in Preview ignores subdivision

  • Would I be missing something obvious in wondering why a Raytrace Preview with the OpenGL Preview renderer selected would ignore subdivision and render the original prop instead?
    0_1528856355732_Screen Shot 2018-06-13 at 12.15.32 pm.png
    Note the raytrace preview has sharp corners and edges.

  • I have cut the front off a box prop to test my script for converting open props to closed, 2-manifold geometry. In doing so, I discovered that the box actually just consists of six squares, with duplicate vertices along the edges. This obviously preserves the box when subdivided, but when I process the open box with front removed, subdividing the now closed surface gives me five disconnected "pillows".

    To avoid the disconnection of the faces, I simply use the Grouping Tool to weld the edge vertices, however, this renders the edges susceptible to smoothing/rounding when subdivided, as the work area image shows.

    The big surprise comes when I raytrace preview it. No subdivision, and sharp corners! Yet the scene preview does show the subdivision. What gives?