UIPageViewController direction only forward

This is the behavior you get when your pageViewController has its transition style set to scroll -- I'm not sure why, but it has something to do with a scroll view being inserted into the hierarchy somewhere (which I could see being allocated if I ran my project with Instruments turned on). If the transition is Page Curl, then you don't get any previous page being displayed if your return nil where you do.

So, I think you're stuck with using setViewControllers:direction:animated:completion: unless you want to switch to the Page Curl animation.