Many fans of the Rosario+Vampire manga really hate the anime series. Gonzo is adapting it rather freely, emphasizing the series’ light, fluffy side at the expense of the manga’s occasional plot. Episode 7 did the most serious continuity damage so far, bringing one of the girls into the story long before she should appear, in a way that would make it difficult to get back on track.
If, that is, they have any interest in using the slow-developing, dark and bloody manga plot. I don’t think they do. Here’s my evidence:
This is the sixth CD-single being released for this 13-episode anime series. There are also several drama CDs, a Moka figurine, a poster, and a Nintendo DS game. And I’m sure there’s more on the way.
They gleefully shredded continuity to bring Mizore in early, because their primary motivation is selling cute-girl merchandise.