Is navigationbar/controller a part of stack of navigationControllers?

Hi,

I have an app with one TabBarController and four tabs. In each tab there's two containerViews which most of them have a navigationController and ViewController.

My issue is that if my first tab has a custom navigationBar of type myNavigationBar and i then move to another tab that doesn't, that NavigationBar implicitly gets the same type.

Is this how it is supposed to be, or have I structured the app in a "wrong" way?