if a nonstandard additive bsp brush collides with a standard additive bsp brush, the surfaces of the bsps break and artifact, causing numerous holes in the brushes.
1. Open Editor (any project)
2. Create two cube meshes
3. Set x to 1000, y to 25 for scale for both (to clearly see the break)
4. Switch to geometry edit mode
5. Grab a single edge of one of the boxes facing towards the other box
6. Press split
7. Grab the edge created closes to the box and the edge created on the far side of the box
8. With the transform widget, move the selection to intersect the other box until it looks similar to the attached image
9. check boxes for faces that have broken
Head over to the existing Questions & Answers thread and let us know what's up.