[ODE] Box/trimesh collision problem

[Brad]

I've got a terrain set up as a grid of trimeshes. When I toss a sphere 
onto the terrain it works fine, and the spheres roll around like they're 
supposed to. If I try to toss a box onto the terrain, it may bounce once 
or twice, but very very soon it'll suddenly shoot up into the air. I've 
also got a plane sitting under the terrain, and I can throw some boxes 
onto that and they bounce and settle fine, then if I toss a box into the 
terrain and the box shoots up in the air, many times the boxes sitting 
on the plane will ALSO shoot off somewhere!

Is this a known issue with ODE? Is there a problem with my code?