User blog comment:Lias' Pawn/BlackBeard Theory 2/@comment-1595565-20140411194149/@comment-24552694-20140412073939

True, the same power cannont exist twice at the same time, yet neither can the one  fruit user have two abilities. thus it stands to reason that BB is only useing the Yami Yami no Mi in some way to simulate WB's Gura Gura no Mi.