ArrayWillChange LiveRecordArray Issue

adapters.application.js

import DS from 'ember-data';
export default DS.RESTAdapter.extend({
  shouldBackgroundReloadRecord(store, snapshot){
  	return false;
  }
});

application.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName:'Ember Twiddle'
});

application.template.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<br>
{{outlet}}
<br>
<br>

index.route.js

import Ember from 'ember';

export default Ember.Route.extend({
  
  init: function(){
  	  this._super(...arguments);
    	$.mockjax({
         url: '/fields',
        responseText: [
          { id: 1, name: 'how', posts: [1] },
          { id: 2, name: 'now', posts: [2,4] },
          { id: 3, name: 'cow', posts: [3] }
          ] 
      	});
    
      $.mockjax({
         url: '/posts',
        responseText: [     
							{ id: 1, name: 'how', utc: '2015-05-12T00:00:00' }, 
							{ id: 2, name: 'now', utc: '2015-05-12T00:05:00' },
							{ id: 3, name: 'brown', field: 3, utc: '2015-05-12T00:02:00' },
							{ id: 4, name: 'cow', utc: '2015-05-12T00:10:00' },
              { id: 6, name: 'six', utc: '2015-05-12T00:35:00' } 
          ]
      });
    
     $.mockjax({
         url: '/posts/2',
        responseText: { id: 2, name: 'now', utc: '2015-05-12T00:05:00' } 
      });
    $.mockjax({
         url: '/posts/6',
        responseText: { id: 6, name: 'six', utc: '2015-05-12T00:35:00' } 
      });
  },
  
  afterModel: function(model){
    this.store.findAll('post');
    model.post.addArrayObserver(this, {
            willChange: 'dependentArrayWillChange',
            didChange: 'dependentArrayDidChange'
        });
  },
  
  model: function(){
    return Ember.RSVP.hash({
        field: this.store.findAll('field'),
        post: this.store.peekAll('post')
    });
  },
  
  dependentArrayWillChange(observedArray, start, removeCount /*, addCount */ ){
    if(removeCount > 0){
      let removedSlice = observedArray.slice(start, start + removeCount);
      console.log(start, removeCount, observedArray.get('length'));
      console.log(observedArray.toArray());
      console.log(removedSlice);
      alert('object removed is ' + removedSlice);
    }
  },
  dependentArrayDidChange(observedArray, start, removeCount, addCount){
    
  },
  actions: {
      unload(){ 
        	 [2,6].forEach(x => {
      	      let record = this.store.peekRecord('post', x);
              if(record){
                this.store.unloadRecord(record);
              }
           });
      },
    	load(type, id){
        this.store.findRecord(type, id);
      }
  }
});

index.template.hbs

<p>This twiddle shows the issues with unloading record from the store and attempting to watch the record array as this is being performed. To see the issue doe the following.</p>
<ol>
<li>click the 'unload' button</li>
<li>View in console the record array state that is printed to screen as records are unloaded</li>
</ol>
<p>
NOTE: on ember data  #5273 the record array will contain null entries indefinitely and immediately, on ember data  #5273 this only happens after the first time the willchange method is called.</p>

<h3>posts</h3>
	{{#each model.post as |post|}}
		<div>Id: {{post.id}}, Name: {{post.name}}, UTC: {{post.utc}}</div>
  {{/each}}

<button {{action 'unload'}}>Unload Id: 2,6</button>
<button {{action 'load' 'post' 2}}>Load Id: 2</button>
<button {{action 'load' 'post' 6}}>Load Id: 6</button>

models.field.js

import DS from 'ember-data';
import Ember from 'ember';

export default DS.Model.extend({
  name: DS.attr('string'),
  posts: DS.hasMany('post', {async: false }),
  postsSorted: Ember.computed.sort('posts','postsSortedBy'),
  postsSortedBy: ['utc:asc']
});

models.post.js

import DS from 'ember-data';

export default DS.Model.extend({
  name: DS.attr('string'),
  utc: DS.attr('date'),
  field: DS.belongsTo('post', {async: true})
});

serializers.application.js

import DS from 'ember-data';

export default DS.JSONSerializer.extend({});
  
  

twiddle.json

{
  "version": "0.4.16",
  "EmberENV": {
    "FEATURES": {}
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "2.16.2",
    "ember-data": "2.18.1",
    "ember-template-compiler": "2.16.2",
    "jquery-mockjax": "https://cdnjs.cloudflare.com/ajax/libs/jquery-mockjax/1.6.2/jquery.mockjax.js"
  }
}