The original object was a box with depth provided by the edges at the top of the box.  he reduced the object down to the three sides you see above that have the smoothing problem.  The 3 faces have a common point and there are only 8 vertexes and three faces in this object.

Poser 5, 6, 7, 8, Poser Pro 9 (2012), 10 (2014), 11, 12, 13