PromiseObject not resolving in template

I have a Model “Content” with DS.belongsTo('medium', {async: true}).

I want to set this field from within a controller, the controller has an object of the right type. But when I .set the property, it becomes a PromiseObject.

The object binding on Handlebars is then updated with <DS.PromiseObject:ember1585>. But it somehow freezes there. It doesn’t update to the right model although the controller already had the Object resolved. So calling {{}} for example always returns an empty string.

Edit: I found the problem and it was a bug on my side. Tried to reproduce it with a gist and found out that it should work that way.