The test map is a single huge model (compared to normal areas, which are in pieces)--this is why the whole map vanishes when you walk past a certain point. It has sections that show scale, sections that play different sounds, rooms with different textures (still couldn't figure out the purpose of that one), a tunnel, and the section Vash mentioned with the overlapping paths. It'll be incredibly useful for future science.
Most importantly, though, is this part:
Recognize it? It's Moatoob. Before they compressed the textures to incomprehensibility (they also made the walls more brown, but digressing).
Vashyron wrote:(I suspect issues in Enemy AI with that.)
That is my suspicion, as well. The only other place I've seen overlapped paths is in a lobby, the Parum west district (the Linear Line entrance crosses under the AMF HQ entrance).