BRepExtrema_DistShapeShape vs BRepExtrema_ExtFP

The above classes behave differently when computing a minimum distance between a vertex and a face. BRepExtrema_DistShapeShape always finds at least one closes point. However, BRepExtrema_ExtFP reports no solutions in some cases. From online documentation is not clear what is the expected behavior of BRepExtrema_ExtFP. Any suggestions?