Poser exports an obj file with vertex and face info, and bodyparts, and materials by name 
bodyparts are identified by a g line and materials by a usemtl line .

I would look to see why the face and blouse have the same usemtl name.

I would check the export options (i dont have poser with me ) and see if there is another option to use the poser material groups names . I usually just have one ticked  and that works fine in Lightwave.