Sideloading funniness

The latest build of Ember.

HTML

<script src="http://builds.emberjs.com/handlebars-1.0.0.js"></script>
<script src="http://builds.emberjs.com/ember-latest.js"></script>
<script src="http://builds.emberjs.com/tags/v1.0.0-beta.4/ember-data.prod.js"></script>
<script type="text/x-handlebars" data-template-name="index">
    <h1>{{name}}</h1>
    <p>
        <button {{action "addToy"}}>Add Toy</button>
    </p>
    <h2>Toys:</h2>
    <ul>
    {{#each toys}}
        <li>{{name}}</li>
    {{/each}}
    </ul>
    <div class="store">
        <h2>DS.Store</h2>
        <p>
            DS.Store has: {{storeToysLen}} toys
        </p>
        <ul>
        {{#each storeToys}}
            <li>{{id}} - {{name}}</li>
        {{/each}}
        </ul>
    </div>
</script>

CSS

body { margin: 10px; }
h1, h2, p, ul { margin: 7px 0; }
h1 { font-size: 1.5em; font-weight: bold}
h2 { font-size: 1.2em; font-weight: bold}
ul { padding: 0 0 0 25px; }
ul li { list-style-type: disc; }
.store { background: #eee; border: 1px solid #666; color: #444; padding: 5px; margin: 50px 10px; }

JavaScript

App = Ember.Application.create({});

// 
// Define models
//
App.Child = DS.Model.extend({
    name: DS.attr('string'),
    toys: DS.hasMany('toy'),
});
Ember.Inflector.inflector.irregular("child", "children");
App.Toy = DS.Model.extend({
    name: DS.attr('string'),
    quantity: DS.attr('number')
});

//
// Main Program
//
App.IndexRoute = Em.Route.extend({
    model: function(){
        return this.store.createRecord("child", {
            'id': childID,
            'name': childName
        });
    },
    setupController: function(controller, model){
        controller.set('content', model);
    }
});
App.IndexController = Em.ObjectController.extend({
    content: null,
    
    storeToys: function(){
        return this.store.all('toy');
    }.property(),

    storeToysLen: Em.computed.alias('storeToys.length'),
    
    actions: {
        
        // Add a toy to the child
        addToy: function(){
            var self = this,
                store = this.get('store'),
                child = this.get('content'),
                toy = nextToy();
            
            // Create toy and add it to the child
            toy = store.createRecord('toy', {
                'name': toy.name,
                'quantity': toy.quantity
            });
            
            // Save the new toy
            toy.save();
        }
    }    
});

//
// Mock a database and web service
//
    
var childID = 0,
    childName = 'Ben',
    toys = [];

// Toy names to cycle through
var toyNameIndex = 0,
    toyNames = [
        'car',
        'doll',
        'teddy bear',
        'xbox',
        'action figure',
        'bike',
        'scooter'
    ];

// Add a toy to the list
function nextToy() {
    if (toyNameIndex >= toyNames.length) {
        toyNameIndex = 0;
    }
    
    var name = toyNames[toyNameIndex++],
        id = toys.length,
        toy = {
            'id': id,
            'name': name,
            'quantity': 1
        };
    
    toys.unshift(toy);
   ...