There's a problem with the way how the polyobjects are constructed on some older Doom wads. The subsector outside the map area where the polyobject walls are placed is not a sector of it's own, but a part of the sector which appears elsewhere on the map

This one is a tough one, it seems like the renderer doesn't support a special "trcik" from the doom engine. I'll have to investigate it further to see how it works.

Fixed.