Yeah that is my guess also - Kabuto, realizing the failure of his old path, decides to join up with everyone else for the gang rape of Madara only to have the 'but this isn't even my final form' pulled after they think he is defeated - that or they were already trapped in a big genjutsu and once they think they beat him, the genjutsu is dispelled and the real battle begins.
While I have really enjoyed Naruto and Bleach, I would have liked if I never heard of them until they had been finished so I could just marathon read all of the story and get to the end.