Yeah I think this is something that should be clarified in the JPA spec. To my knowledge, JPA has not been fully transfered to the EE4J project yet, so yes, that would be the correct repo for the time being.
Could you test the model and query with EclipseLink and post here how it behaves? I would assume that it also renders a join. If not, chances are good that we can change this without violating the spec/TCK.