New Twiddle

application.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  myComponent: 'will-destroy-element',
  appName: 'Ember Twiddle',
  actions: {
    click() {
      if (this.get('myComponent') !== null)
        this.set('myComponent', null);
      else
        this.set('myComponent', 'will-destroy-element');
    }
  }
});

application.template.hbs

<h1>willDestroyElement and component helper bug</h1>
<br>
When a component is rendered with the <i>component</i> helper <i>willDestroyElement</i> is called after the element is removed from the DOM.<br>
The component below is rendered twice, once with the component helper and once inside an if block.<br>
The component's <i>willDestroyElement</i> hook logs to the console whether or not it's contents exist in the DOM.<br>
Pressing the button below will cause both components to be removed from the page.<br>
It is expected that <i>true, true</i> will get printed to the console, but <i>false, true</i> is printed instead.
<br>
{{component myComponent}}

{{#if myComponent}}
{{will-destroy-element}}
{{/if}}
<br>
<br>
<button {{action 'click'}}>Toggle</button>

twiddle.json

{
  "version": "0.6.0",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.3.1/ember.debug.js",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/2.3.3/ember-data.js",
    "ember-template-compiler": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.2.0/ember-template-compiler.js"
  }
}

will-destroy-element.component.js

import Ember from 'ember';

export default Ember.Component.extend({
  willDestroyElement() {
    console.log($.contains(document, this.$('#gone')[0]));
  }
});

will-destroy-element.template.hbs

<h4 id="gone"> Will Destroy Element</h4>