Ember loading state not triggered in transitionTo

If I use a transitionTo on a route with a slow model hook, the loading.hbs state never gets triggered. (I have loading.hbs templates at every level in the hierarchy.) If I refresh the page, the loading state gets triggered just fine.

During the transitionTo call the page just stays on the previous route until the promises in the model hook resolve, and then it transitions to the other route. Is this a known behaviour for transitionTo?

Side note -- the model hook returns an Ember.RSVP.hash with 3 API calls, that each return promises. I have tried simplifying this model hook to return a simple promise with a timeout, with no luck.