[ODE] Can't seem to make parallel opposing planes

[Tim Rightnour]

I'm attempting to bound the edges of my heightmap terrain with planes, to keep
my NPC's from falling off the edge of the world like Christopher Columbus did. 
I decided to fiddle with it a little first in test_boxstack.cpp, and found I
couldn't make it work.  I can put two, or even three perpendicular planes up,
but if I place one opposite another, the behavior becomes bizzare.

For example, two planes, opposite eachother, one with a negative normal, and
the other positive, creates a wierd wall on the positive side, where all
objects probably fit into the small ContactSurfaceLayer and jiggle thier way to
the ground, as if they were being sandwiched between two planes that were
directly on top of eachother.

I assumed initially that I just got the normals and d wrong, so I tried all
possible combinations of the two opposing planes, but couldn't make it work. 
Is there a bug in planes, or am I doing something stupid?

  dCreatePlane (space,0,0,1,0);
  dCreatePlane (space,-1,0,0,-1); 
  dCreatePlane (space,1,0,0,1);


---
Tim Rightnour <root at garbled.net>
NetBSD: Free multi-architecture OS http://www.netbsd.org/
NetBSD supported hardware database: http://mail-index.netbsd.org/cgi-bin/hw.cgi