Plasmacam Issue With .DXF Import

I'm a tech ed. teacher and one of my assignments has my students create an extruded object in Autodesk Inventor, export the face as a .dxf file, and import this .dxf file in Plasmacam. Most of the time it works just fine. However periodically we get these stray lines that connect to the origin of the cut area as shown in the image. I have not found an obvious reason for these lines nor have I been able to get rid of them consistently. Anyone else seen this or have suggestions?

What image?