To the point: http://i49.tinypic.com/xc7ds.jpg
Particles with a sub-emitter "on collision", are not colliding with planes, but rather, colliding as though the plane stretches on infinitely.
The picture is some falling cinders, and they have an 'impact' sub-emitter built to go off upon collision.
When I click the '+' symbol to generate a plane, the particles not only hit the plane, but also the entire area to X,Z, far beyond the plane.
Anyone had this or can show me a pic of particles colliding only with their designated plane (and how you did that...)? I can toss a Prefab/Scene onto rapidshare or something if people want to see this glitch for themselves.