Look at this Tut: http://tapetube.com/2009/10/importing-iges-into-modo-moi-3d
There is everything explained even in the comments, that MoI exports a vertex-map that could mess things up.
Even like the users in the comments I would def agree that there has to be something for switching on/off the export of this vertex-map in the export dialog which really makes no sense in modo and could disturb newbies, as there is a toggle function for smoothing in Modo by default.