Why is Zero???

application.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  foo: 0,
  
  actions: {
    toggle(property) {
      this.incrementProperty(property);
    },
    
    reset(property) {
      this.set(property, 0);
    }
  }
});

application.template.hbs

{{!--
Outside foo: {{foo}} <br>
Outside readonly foo: {{readonly foo}} <br>
Outside unbound foo: {{unbound foo}}
--}}

<hr>

{{change-foo originFoo=foo 
						 unboundFoo=(unbound foo)
             readonlyFoo=(readonly foo)}}

<hr>

<button type="button" onclick={{action "toggle" "foo"}}>
	Update Original Foo from Outside
</button>

<button type="button" onclick={{action "reset" "foo"}}>
	Reset to 0
</button>

change-foo.component.js

import Ember from 'ember';

export default Ember.Component.extend({
  didReceiveAttrs() {
    this._super(...arguments);
    console.log('Receive: ', this.get('unboundFoo'));
  },
  
  didUpdateAttrs() {
    this._super(...arguments);
    console.log('Update: ', this.get('unboundFoo'));
  },
  
  actions: {
    update(property) {
      this.incrementProperty(property);
    }
  }
});

change-foo.template.hbs

Original foo: {{originFoo}} <br>
Readonly foo: {{readonlyFoo}} <br>
Unbound foo: {{unboundFoo}} <br>

<br>

<button type="button"
				onclick={{action "update" "readonlyFoo"}}>
  Update Readonly Foo from Inside
</button>

<button type="button"
				onclick={{action "update" "unboundFoo"}}>
  Update Unbound Foo from Inside
</button>

{{yield}}

twiddle.json

{
  "version": "0.10.5",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": true,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "//cdnjs.cloudflare.com/ajax/libs/jquery/3.1.1/jquery.js",
    "ember": "beta",
    "ember-data": "beta",
    "ember-template-compiler": "beta",
    "ember-testing": "beta"
  },
  "addons": {}
}