I haven’t exactly figured out what is causing this inside of Ember, but it appears to be instantiating the base class controller instead.
Ember Latest - JSFiddle - Code Playground (Line 33) if you change App.PanelController to Ember.ObjectController it uses to correct controller.
Has anyone else encountered this? I’ll submit an issue on github and hopefully a pull request once I get to the bottom of it.
Update: So it looks like it is in fact using the correct controller it’s just controller object is ToString-ing to the base controller.