I imagine it's the same as any computer assisted art form. Anyone could generate a poem from a random list of words, doing no actual work themselves (other than curation?). But since they'd be the one who published it, they'd get the copyright.
Until someone designs an AI that's smart enough to compose music and convince the world it should count as a sapient being and win the lawsuit to secure the rights to the song and convince the world not to destroy it out of fear of a full-blown T2: Judgement Day scenario, that's not going to change.
And let's face it, securing the rights to a pop song is a pretty dumb reason to risk outing yourself as a technological singularity.