Nonsensical deux de machina device used to create a common link between the three Robotech Sagas together.
The best explanation that you'll ever get from Protoculture is from the novelizations/original novels from the Brian Daley/James Luceno tandem. Obviously, being able to write without the restriction of being a half-hour show helps them out a lot. I don't think their explanation is canon, though.
The story I've heard is that Southern Cross was actually cancelled and thus never had a proper ending, and so the Robotech "creators" needed another show to bring the total number of eps to the magical syndie number of 65, and thus, Mosepeda was tacked on.
Anyways, "The Masters" sticks out like a sore thumb as far as the three Robotech generations go, and like Jason X I'd say to just get Southern Cross and be done with it. The other two are fine to watch in their Robotech versions.