I am using the controllerAs syntax.
I used $controller to inherit from a parent (more like a base or abstract) controller. I found this question not long ago which I based on.
I noticed that when I use a function which uses a controller property (this.propName), it does not use the current controller this, but the parent's. Here's a demo (plunkr).
Here's a gist to both my parent controller and child controller.