Nope, see 's first post about editing the mesh normals. The idea is to have uniform shading across all of your grass, rather than have normals on the planes that face away from each other.
Again, that’s for a single tree object. On a grass plane, you want them to all face the same way, as the grass is supposed to be one huge object, not a collection of small objects. A quick lighting re-build seems to have fixed my problem, bit odd though.