deleting object key fails to update child component templates

components.my-comp.js

import Ember from 'ember';

export default Ember.Component.extend({
	options: Ember.A([
    {name: 'aa', id: '123'},
    {name: 'bb', id: '456'},
    {name: 'cc', id: '678'},
  ]),
  
  selected: null,
  
  init(){
    console.clear()
    this._super(...arguments)
    
    this.set('selected', Ember.Object.create({}))
  },
  
  actions: {
  	
    toggleItem(item){
			const selected = this.get('selected')
      if (selected[item.id]){
        delete selected[item.id]
        this.notifyPropertyChange('selected')
      } else {
        selected.set(item.id, item)
      }
    }
    
    
  }
});

components.option-item.js

import Ember from 'ember';

export default Ember.Component.extend({
});

controllers.application.js

import Ember from 'ember';

export default Ember.Controller.extend({

});

templates.application.hbs

{{my-comp}}

templates.components.my-comp.hbs

SELECTED:

{{#each-in selected as |id s|}}
	<li>
		{{s.name}}
  </li>
{{/each-in}}

<br/><br/>

OPTIONS - same component, remove button updates correctly:
{{#each options as |item|}}
	<li>
		{{item.name}}
		<button {{action 'toggleItem' item}}>
    	{{#if (get selected item.id)}}
      	REMOVE
      {{else}}
      	ADD
      {{/if}}
    </button>
  </li>
{{/each}}

<br/><br/>


OPTIONS - child component, remove button doesn't update:
{{#each options as |item|}}
	{{option-item
  	item=item
  	selected=selected
    toggleItem=(action 'toggleItem')
  }}
{{/each}}

templates.components.option-item.hbs

<li>
		{{item.name}}
		<button {{action toggleItem item}}>
    	{{#if (get selected item.id)}}
      	REMOVE
      {{else}}
      	ADD
      {{/if}}
    </button>
  </li>

twiddle.json

{
  "version": "0.12.1",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "use_pods": false,
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.12.0",
    "ember-template-compiler": "2.12.0",
    "ember-testing": "2.12.0"
  },
  "addons": {
    "ember-data": "2.12.1"
  }
}