Here's how you avoid it:
I am guessing a lot of the bleeding comes from rays that pass by the edges of a face and "miss" hitting it. CS2 had this problem.
When lightmapping a face, don't consider it a triangle, just consider it an infinite plane. You should be tracing rays onto this infinite plane, over an area a little wider than the face you are lighting. Anything in front of the plane will cast a shadow, and anything behind the plane we don't care about, since that wouldn't affect the triangle.
I am guessing a lot of the bleeding comes from rays that pass by the edges of a face and "miss" hitting it. CS2 had this problem.
When lightmapping a face, don't consider it a triangle, just consider it an infinite plane. You should be tracing rays onto this infinite plane, over an area a little wider than the face you are lighting. Anything in front of the plane will cast a shadow, and anything behind the plane we don't care about, since that wouldn't affect the triangle.