Setting terrain_chunk to 0 is not supported by A8. Yes, it disables chunking as in A7, but some A8 subsystems, such as collision, only support chunked terrain. Therefore we'll have to do something about terrain_chunk = 0 in a future version. It was a leftover from the past and should be disabled.

A case where c_updatehull is required is when the terrain is deformed and something does a terrain collision within the same frame. Then you must call c_updatehull directly after the deformation for preventing collision problems before the engine updates the hull. The engine updates it only at the end of the frame cycle.

I believe the duplicated terrain vertices are automatically updated when normals are directly set. But I'll check this to be sure.