User blog comment:Xilinoc/Ch. 577 - SWORD/@comment-11446176-20140416080500/@comment-24429517-20140418092529

I think what happened with Kenpachi's shikai was that it was an incomplete skikai, because it was never formed from an Asauchi he had a his sword before becoming a shinigami. So his sword up till now was kind of like Ichigo's very first sword in the sense that it was a permanently released skikai but an imcomplete one and just like how Ichigo had to talk to Zangetsu and learn his name to fully release him Kenpachi might have gone through a similar process. So maybe what we're seeing now is his true shikai and the release command is there because he now has complete control over his sword. (and carrying around something like that is impossible) Just my opinion.