Packaging an object for a model with a dynamic route is undefined — why?

Playing around with with EmberJS, and I'm trying to understand some behaviour with routes right now.

I'm building a test app with the intention of hooking into the Rdio API and displaying albums/songs for various artists.

Right now, there are only two views: The Index (a listing of all available albums), and an individual Album view.

The dynamic route is defined like so:

App.Router.map(function() {
  this.route("album", { path: "/album/:key" });
});

And given a fixture that looks like this...

App.ALBUMS = {
 "status": "ok", 
 "result": [
  {
   "key": "a5337866", 
   "icon": "http://ift.tt/18vcQPe", 
   "artist": "The Decemberists", 
  }, 
  {
   "key": "a5229271", 
   "icon": "http://ift.tt/18vcOam", 
   "artist": "Nicki Minaj", 
  }, 
};

...the index works just fine:

App.IndexRoute = Ember.Route.extend({
  model: function() {
    return {albums:App.ALBUMS.result }
  }
});

(I've intentionally packaged App.ALBUMS.result in an object so that I can pack more information into it later.)

However, when I get to the Album view, I get a problem:

App.AlbumRoute = Ember.Route.extend({
  model: function(params){
    console.log(params);
    console.log(App.ALBUMS.result.findBy('key',params.key)); //Logs object just fine
    return App.ALBUMS.result.findBy('key',params.key); //ERROR
  }
});

Packaging that return value (which should already be an object) in a second object or array though, and it works.

// THIS WORKS!: 
return [App.ALBUMS.result.findBy('key',params.key)]; 
// THIS AlSO WORKS!:
return {album: App.ALBUMS.result.findBy('key',params.key)}; 

Why?

The error itself is rather unhelpful:

     Error while processing route: album undefined is not a function TypeError: undefined is not a function
    at EmberObject.extend._setupArrangedContent (http://ift.tt/18vcOqA)
    at null._arrangedContentDidChange (http://ift.tt/1yykQUE)
    at applyStr (http://ift.tt/18vcQPi)
    at sendEvent (http://ift.tt/1yykRYQ)
    at notifyObservers (http://ift.tt/18vcQPo)
    at propertyDidChange (http://ift.tt/1yykQUL)
    at iterDeps (http://ift.tt/18vcQPq)
    at dependentKeysDidChange (http://ift.tt/1yykSfa)
    at propertyDidChange (http://ift.tt/18vcOqL)
    at iterDeps (http://ift.tt/18vcQPq)