User blog comment:IamJakuhoRaikoben/Chapter 450: Alone in all the World, Review./@comment-25111584-20150901154629

So ... it's pretty much certain Zeref and Mavis are actually afflicted with a Curse rather than possessing a Magic which they can't control really well.

If that's the case, I wonder what explanation will be given form Moon Drip not working on them. It can dispel anything, right? Imo (as a biased Ur fanboy maybe /o/), it'll just be poor writing if we're told Moon Drip is not powerful enough to dispel the Contradictory Curse. .-.