I gave up with BSP in DBPro a while ago, there appears to be many issues with it. I think the majority of the problems are collision related rather than display related.
Kensupen wrote an excellent .x object sliding polygonal collision routine which allows you to collide against .x objects and i've turned that into a suite of functions that lets you use them much like BSP commands.
You will find Kensupens code in the code snippets, and my code on my web page under Utils\Programmers Resource.
http://www.bansheestudios.com
Pneumatic Dryll
