Are you triangulating the mesh before you save it out? A mesh that has quads will not always calculate the lighting normal correctly because the vertices for a quad are not alway planar.
To fix it: in W3D so I choose the "Face" mode for the object, select all faces with rubber band box, right click on open area, click on "Tesselate", and choose "Triangulate". That usually fixes the problem. The vertices of each triangles are planar and the lighting normal is correct.
Another thought: you can also select individual "problem" quads and triangulate them.
To fix it: in W3D so I choose the "Face" mode for the object, select all faces with rubber band box, right click on open area, click on "Tesselate", and choose "Triangulate". That usually fixes the problem. The vertices of each triangles are planar and the lighting normal is correct.
Another thought: you can also select individual "problem" quads and triangulate them.