Hexagon may be doing what some other 3D apps' default OBJ import do: treating groups as separate objects.  In reality, Poser does the same thing for figures when it creates body parts, but it isn't something you need to consider.  When this happens, shared vertices are duplicated and usually vertex order is lost.

Think of a Wavefront OBJ file as two basic areas: a vertex list (this includes UV texture vertices (vt) and normals (vn)) and a facet list (polygons (f)).  Groups (g) and materials (usemtl) only group facets (no matter where these are defined) and vertices are assigned by index to the facets.

You are correct that morphs are only interested in the vertices and nothing else.  The most important part here is that vertex ordering and count should be maintained.

C makes it easy to shoot yourself in the foot. C++ makes it harder, but when you do, you blow your whole leg off.

 -- Bjarne Stroustrup

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