BSP brushes break when non-standard subtractive bsp brushes are used

if a nonstandard bsp brush is used as a subtractive brush, additive bsp brushes will break and show incorrect holes when in contact with the subtractive bsp.

1. Open editor
2. Create a bsp box
3. Create a subtractive bsp cone
4. Switch to geometry edit mode
5. Grab a vertex of the subtractive brush, move it to a new position that intersects with bsp box