I think the problem is related to the nature of the UIPageViewController. It is built from UIScrollView. I don’t know exactly why weird resizing occurs, but it is especially noticeable when the view controllers that make up your pages use auto-layout. Apparently, blocking the restrictions in your pageview dispatchers on the supervisor forces the elements to resize after the transition, because the supervisor itself gets resized after the specified transition.
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http://www.appcoda.com/uipageviewcontroller-storyboard-tutorial/