User blog comment:Xilinoc/Ch. 615 - All is Lost/@comment-6073876-20150212163151/@comment-5398287-20150212194558

Well (according to TvTropes, at least) Kubo originally intended to have Urahara revealed as the villain at the end of the SS arc, and Aizen was gonna be dead for real; about halfway through, he decided to have Aizen be the bad guy because he found it more interesting, so he started up the subplot of the mystery surrounding Aizen's death. That's why Urahara acted kinda shady during the first arc.