Just so it's clear, the RSR files DraX suggests could be the problem are not the RSRs that produce the thumbnails in your selection folders. This is an RSR file is associated with the OBJ file. I believe it is generated and can sometimes generate in a funky manner which will make the OBJ behave strangely. Deleting this RSR file (located in the Geometries folder) corrects the problem as a new RSR is generated if necessary. I say if necessary because I'm not sure what criteria makes the RSR generate. It doesn't happen for every OBJ. So MAC or not, it may really bear looking into to see if an old RSR is the culprit here. It would make more sense for a MAC not to use the RSRs that are for thumbnails than for it not to produce the RSRs that are generated for geometry files.