[ode] Object 'boil' in BoxStack - edge to plane intersections???

[John D. Gwinner]

I'm noticing some instances where two objects in test_boxstack will
'boil'; I think it's from edge to surface intersections.  After a while
the objects 'bounce' off of each other and fly away.  It's almost as if
an error term is building up and finally bounces the objects away from
each other.  It's an odd instability.

(surface to surface or edge to edge doesn't seem to do it).

Is this an accurate collision detection issue, or is there some
parameter I can change to avoid this?

To duplicate this, start boxstack and drop a bunch of blocks until you
get a flat one resting on another one; stop dropping items and wait a
while.  Eventually the two leaning against each other will start
bouncing and will then jitter; and might 'explode'.  It looks like they
are boiling.

It's not every intersection, but I think I can see it being only on edge
to plane intersections with boxes.

(this is different than the case in the same simulation where a new item
gets dropped 'inside' of another, i.e. penetrating from the start -
those objects explode away which is what I'd expect.)

               == John ==