Custom Unwind Segues in UINavigationControllers

I'm trying to trigger a custom unwind segue from a button in my second view controller (not the UINavigationController's back button).

If the view controllers are not embedded in a UINavigationController, everything works fine. If they are, things go a little wonky.

What I'm expecting

If you open MainStoryboard.storyboard and delete the main UINavigationController then run the app, everything works as expected.

Tap the button to go to the second UIViewController, then tap either of the UIButtons to trigger the unwind segue.

You'll get the following in your Console:

What actually happens

Undo the above changes, so the UINavigationController is back in the storyboard. Then run the project again.

Do the same thing as last time, and notice the difference in the Console:

It's fixed!

After submitting a request to Apple DTS, they suggested I use a UINavigationController subclass. That worked.

See the working version in the DTS_Response branch.