How Do I Maintain Resource Type When Converting a P3 Project

When I convert a P3 project to P6 the resource types don't necessarily stay the same. i.e, In P3 a resource type might be Labor but after converting the project to P6 it turns to Nonlabor.  I was told that if I wanted it to come over as Labor I needed to blank out the Units field in the P3 Resource dictionary.  This is never consistant for me.  Does anyone know how to maintain the Resource Type when converting a project?