When using the column based split view controller, it presumes that clients want a navigation controller in each of its non-compact columns and will wrap a view controller in one of not provided. This is primarily so that collapsing (when it moves from multiple to single column) behaves deterministically and automatically. So what is happening is you're getting a tab bar controller wrapped in a navigation controller with additional navigation controllers inside – and thus double navigation bars. Realistically this may be a case where you want to create your own custom view controller container instead of using UISplitViewController, as I'm not sure how many of the edge cases you would hit might be resolved.
Topic:
UI Frameworks
SubTopic:
UIKit
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