I've got a question for you, I've found some piece of code inside EntityEx.Physics that I have some doubts about, inside the Physics method:

		// Floating item bobbing motion (special1 is height)
			if (Sector->bHasExtrafloors)
			{
				//	Make sure FloorZ is from bottom region.
				Origin.z = ONFLOORZ;
				LinkToWorld();
			}

These make weapon (and other) pickups in Korax Arena to be spawned inside the extra floors and make the player unable to pick them up. Is there a reason for this code to be here? I don't quite understand the need of keeping it there.

Without it floating bob items will try to bob using current FloorZ, and if it's above a 3D floor it's wrong because thing's z value is specified against bottom floor.