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Summary:
When a UIViewController which is embedded in a UINavigationController presents its own modal, the UINavigationBar shrinks in size so that the portion that would be underneath the status bar is made clear

This can be reproduced in the iOS 11 Apple Music app’s Now Playing modal (video attached). I’ve made a library to replicate that transition, which doesn’t touch the presenting View Controller or it’s view hierarchy at all, and this bug can be replicated in that, so it’s an issue with UINavigationBar and not the Apple Music transition either.

Link to the same issue with my library: https://github.com/HarshilShah/DeckTransition/issues/28

Steps to Reproduce:
1. Open the iOS Apple Music app to any tab with a UINavigationBar visible
2. Press on any item (one of the top menu items such as Playlists, Artists, etc., or an album from within the Recently Added section)
3. Scroll down a bit so that the area under the status bar isn’t empty
4. Press the now playing bar to open the full modal

Expected Results:
The only change in the presenting view is that it shrinks

Actual Results:
The presenting view shrinks in accordance with the transition, but the UINavigationBar also shrinks to reveal the content underneath the top 20 pixels i.e. where the status bar would be

Version:
iOS 11 beta 5

Notes: