Hi gui, for OBJ export it may help if you set the option for "Output: Quads & Triangles" in the Meshing options dialog that shows at export time from MoI, instead of "Output: N-gons".

Some programs have difficulty dealing with complex n-gons, meaning polygons having more than 3 or 4 sides.

If that does not help, can you give some more details about the erratic behavior you're seeing like a screenshot?

Thanks, - Michael