Update: I have decided to go a different route with my problem. Instead of trying to reuse the same UIViewController directly, I use two vanill
Definitely a bug in Storyboards. Another way to do this is to create basic UIViewControllers for each UINavigationController, then have a UIContainerView that points to the same UIViewController in each of the basic view controllers.
UIViewControllers
UINavigationController
UIContainerView
UIViewController