Torque Crashes Upon Lighting

Hey, all! If anyone could help me out, I would be most appreciative.

I have an issue that when TGE attempts to light the scene with this DIF, Torque immediately crashes. No errors or anything in the log. The same DIF file was tested under Linux, Windows, and Mac. And Torque crashed on both the Windows and Linux systems, but was perfectly fine on the Mac.

The map in QuArK is sub-divided into seven groups, in this order:
Floor
window and door closures
ceiling
Lights
trim
atrium
Walls

All the negative polygons in the map are at the bottom of the Walls group.

If exported to DIF from QuArK, with everything but the Walls (i.e. Walls is set to "ignore to map builds"), then it'll work.
If it's only the walls, it'll work.
Also, if it's everything except the Floor, it'll work.
(However, with everything, it doesn't work.)
There appears to be some sort of conflict when the Floor and the Walls are in there at the same time.

The DIF in question can be found at cs.nmu.edu/vnmu/temp/lighting_issue.zip

Are there any know issues possibly related to this?

QKM file available upon request.

Update: Alright, after toying around, the issue has been fixed by moving the ordering of the groups... Floor is now immediately above Walls in the ordering. It is now as follows:

window and door closures
ceiling
Lights
trim
atrium
Floor
Walls

However, I would still like to know why this fixed it.
Thanks in advance for any help you can offer! ^_^