Keynote no longer goes into Presenter Notes mode automatically My Keynote presentation setup used to work like this: 

My Macbook and the the projector are set to mirror one another. When I press Play in Keynote, Keynote used to split the presentation with the presenter view on my Macbook and the audience view on the projector. 

Now, however, it just stays in mirrored mode. So I have to exit the presentation and go into System Preference and make the change in Displays. It's very annoying when the presentation includes a demo and I'm constantly switching things up every time I go in and out of the presentation.

I could have sworn that Keynote used to be smart enough to do this for me... which was quite graceful! What happened? Is it a setting somewhere? Am I misremembering?
In Keynote version 6.6:


Keynote > Preferences... ⌘+,
Slideshow tab
Tick the Enable Presenter Display check box


Then go to Play > Customize Presenter Display... to be sure the output is as you expect.