I guess there is a bug with the {{with}}
helper, because if you use the {{#each elem in model}}
and update the {{with}} to use the elem
variable: {{#with elem.orders.order controller='ordersIndex'}}
all works.
This is the updated orders/index
template:
<script type="text/x-handlebars" data-template-name="orders/index">
<div class="inline-headers">
<h4><label>Brokerage: </label>{{titleize brokerage}}</h4>
</div>
{{#each elem in model}}
<h4 class="account-header"><label>Account: </label>{{account_number}}</h4>
{{#with elem.orders.order controller='ordersIndex'}}
{{partial "_orders_table"}}
{{/with}}
{{/each}}
</script>
And this is the updated jsbin http://emberjs.jsbin.com/piwuyare/1#/orders