Bill,
Have you tried exporting the file as R12 AutoCad version of the DXF? I use Rhino too, and it uses NURBS (Non-uniform Rational B-Splines) as it is method creating models. Rhino is great! NURBS saves a lot of space when creating models, because it is a mathematical short-hand for curves. Saving as an older version of AutoCAD shoulld avoid the problem. My bet would be that Rhino is taking a shortcut for the duplicate and that is causing the problem. If that doesn't work, post a copy of the DXF and someone here can try to convert it to get good toolpath on it for you.
Ergoman