Ember: binding controller properties to query parameters

I know ember is supposed to have some built-in binding of controller properties and query params. Docs state (referring to a previous example):

once the articles route has been entered, any changes 
to the category query param in the URL will update the 
category property on controller:articles, and vice versa.

I take "vice versa" to mean that if there's a change to one of the controller properties, it would also be reflected in the QPs on the URL. perhaps I am mis-interpreting that. But if my interpretation is correct (it's probably not), it's not what's actually happening.

I put together a twiddle to demonstrate

Is there a way to bind the QPs on the url to the controller properties so that

a) the controller properties update if the url QPs update

b) the QPs in the location bar update if the controller properties update

?

Any help appreciated