It seems to me that the method used to export a way or a track or path from JOSM to GPX works not fine.
Really it is designed mainly to export a relation. When I select ONLY a path the export procedure generates a GPX file that contains not only my path but also all the elements of the group which the path belongs to and I did not find a way to separate or eliminate the unwanted elements.
Does anybody know a way to export JUST the wished element?
Enable expert mode, copy the way, create a new layer, use paste at source position, export to gpx. Does this work for you?