Manta Climbing Walls (Bug/Feature) UT2004

Maybe someone know what the problem from this one is and how to avoid or cause it.
Here is a topic with sampled informations so far. But it's still not solved.
http://ceonss.net/viewtopic.php?f=14...p=16500#p15659
In the last post I made a minimum working example.
From a new file.

• I have one big Substract Brush (7168x32768x24576).
• Two PowerCore, Two playerstart, Two Manta, one ZoneInfo, One LinkSetup.
• Than one other Substract Brush (256x256x265). I just moved the brush. It was created when the BuilderBrush was on the side.
• When the small is above the big, the Bug is there also when not connected.
• When on the side it's away.
• When under it's there.

I don't get why it appeared as there are maps which are build exactly the same (Big Brush and on top other Brushes for Sky). I tryed to create the Bug there, but without success.
https://youtu.be/N3HM-B8r29k

Very weird. I have no idea.