Brenda Chapman would have been Pixar’s first female director, but I would assume the change had nothing to do with her gender. Regardless, I’m willing to bet that a controversy is in our midst.
Brew also reports that One Man Band director and story vet, Mark Andrews, is actively replacing Chapman in the role of helmer. No further details were mentioned as to why a change was implemented.
As you may know, directorial swaps aren’t anything new at Pixar. I’d point to Toy Story 2, but the best example is Jan Pinkava’s flailing Ratatouille which was subsequently turned into an Oscar-winning masterpiece by Brad Bird.
Hopefully, everything was done for the best— you can trust Pixar on that end. We wish Brenda Chapman the best of luck in her future endeavors, assuming the news isn’t simply hogwash.
Update: I’m glad to report that Brenda Chapman has NOT left Pixar Animation Studios. However, The New York Times confirms confirms today that she has stepped down as director on Brave. A Disney rep commented, "the decision to remove her was made for “creative reasons.”