Older versions of MotionBuilder (versions 2010 and earlier) do not support Geometry Vertex Normals and can present issues with edge definition.
If you are using an earlier version of MotionBuilder and this problem occurs, you must activate the Split per-vertex Normals option. When you activate this option, geometry vertex normals are split based on edge continuity. Vertex normals determine the visual smoothing between polygon faces. They reflect how 3ds Max renders the polygons in smooth shaded mode.
This option only applies to older MotionBuilder workflows to ensure visual fidelity of surface continuity. It lets you transfer hard edge information to MotionBuilder.
Use this option to preserve whether edges are hard (divided) or not (continuous) when you operate between 3ds Max or Maya and MotionBuilder 2010 and earlier. If you disable this option, all smoothing groups in 3ds Max are ignored as well as all hard/soft edge information in Maya.
For example, a 3ds Max-created box that would normally have defined edges would lose them, with all faces visually connected, without visible edges dividing them, in MotionBuilder 2010 and earlier. This is result is hardly noticeable for organic objects, but is very noticeable on hard surfaces such as tables and cars, and so on.
See the Split per-vertex Normals section for a workflow to import FBX files exported from 3ds Max into MotionBuilder with proper edge continuity while retaining the original 3ds Max edge continuity for import back into 3ds Max.
