I have also some problem with it when doing chunked terrain vertex manipulations... I found an idea in a 256k contest entry named MathHero that:
ent_fixnormals(terrain_entity,0);
and
c_updatehull(terrain_entity,0);
can work, with 0 instead of 1. It is not documented too, what it does exactly.
but I found ent_fixnormals work well only with A7 in this way, it gives no good result in A8 (terrain shading seems to have different implementations in the 2 engines). finally I wrote my own tiny script for setting vertex normals thus getting proper (and a bit stronger) terrain shading...