Nurbs, 2x2, when i rebuild it with 3x3, it works, when i downsample it to 2x2 again it stops working. Also, i have turned one of the height edges of the box into a line along which i distributed planes. When i intersect this (2x2) surface with them, the sections don't go all the way through. As with the bounding box, rebuilding with a higher resolution, it starts working fine again.