Is it possible that the "bendix" you have isn't OEM? When my starter was rebuilt some years ago, the electric shop used a generic one, and while it bench tested just fine, it didn't work in situ; in fact, it didn't disengage at all. The restorer took it out, cleaned it all up and tried again--same thing. Finally he removed it once again, had a Bosch unit put on and all was well.
Food for thought in case you don't know the origins of what you have.