cp not updating when using hasMany(..).value() instead of get(..)

I created a jsbin: http://ift.tt/1Wi8CB5

Issue: cp characters on post does not get updated when property content changes on comment.

'Fix': the change does happen when using this.get('comments') instead of this.hasMany('comments').value().

get notifies observers that it should look for changes on the property because it is being used, while hasMany does not seem to have this functionality..

Is this on purpose or a bug?