Defictionalization: The series itself originally only existed as a fictional manga/anime within Genshiken. When Genshiken's anime adaptation was released on DVD, three episodes of Kujibiki Unbalance were included as OVAs (which are meant to be the first episode, a Clip Show, and the second-to-last episode of the fictional anime). It eventually became popular enough on its own to be made into a real 12-Episode Anime and manga that follow a different continuity.
Completely flipped in the English dub, where every character retains their voice actor from the OVA's, with one exception. The odd one out? Ritsuko.note (the recast was due to Jessica Calvello's retirement; however, new CV Anna Morrow was such a dead-ringer for Ms Calvello that most people wouldn't notice a difference)