Unwind segue not firing in Xcode 8 GM using Swift 2.3

Question

I'm having an odd problem with Xcode 8GM + Swift 2.3.

Creating an unwind segue - like I've done a million times before (before upgrading) - it seems as though the segue isn't fired.

Here's a simple project showing the issue: https://github.com/Jeraimee/unwind_testing

Here's the steps I (always) use:

1. Create IBAction in the controller I want to unwind to.
2. In the scene I want to unwind from, CTL+drag the controller icon to the exit icon.
3. Select the IBAction I created in step 1 (with "withSegue:" appended).
4. Select the 'Unwind segue to "Exit"' I just created in the outline view.
5. Add an identifier to the segue.
6. Add IBAction via assistant editor for a button on the page.
7. In the IBAction created in step 6 add: self.performSegueWithIdentifier("identifierFromStep5", sender: self)

This doesn't seem to be working anymore so... what am I missing?