[2.2.8-2.2.9 RC2] Polyobject flats in skybox render over FOFs

I discovered an issue with the software renderer not too long ago. If a level uses a skybox that has polyobjects in it, then the flats of those polyobjects will render on top of FOFs in the normal traversable area of the level. The polyobject flats won't render through non-FOF level geometry, and tweaking video settings doesn't seem to change anything.

In both 2.2.9 release candidates, the rendering issue seems to be dependent on the camera's distance from the FOF.

2.2.8:

2.2.9 RC1/RC2:

Test WAD: epic_polyobject_fail.wad