Binding a related model inside a partial and saving it

I have a customer record and it in turn has an address.

template:

address-form partial:

Inside the partial I can do and this works (it picks up the value entered into the input box).

However, back in the parent template I can do but this results in undefined.

In the route, the address isn't populated:

window.console.log(this.currentModel.get('address')); //undefined

Regular attributes for the currentModel in the route do work.

What am I doing wrong?