genemu_jqueryautocompleter_entity with AJAX route_name setting JSON as value

I use genemu_jqueryautocompleter_entity inside the LexikFormFilterBundle:

        $builder
            ->add('branch', 'genemu_jqueryautocompleter_entity', array(
                'route_name' => 'ajax_branch',
                'property' => 'name',
                'class' => 'PlusquamContractBundle:Branch',
                'required' => true
            ));

My AJAX Controller according to the route:

    /**
     * @Route("/branch/ajax", name="ajax_branch")
     */
    public function ajaxAction(Request $request)
    {
        $value = $request->get('term');

        $em = $this->getDoctrine()->getEntityManager();
        $branches = $em->getRepository('AppBundle:Branch')
                      ->findByName($value);

        // Get branches by user if non-admin

        $json = array();
        foreach ($branches as $branch) {
            $json[] = array(
                'label' => sprintf('%s (%s)', $branch['name'], $branch['company_name']),
                'value' => $branch['id']
            );
        }

        $response = new Response();
        // better way to return json - via header?
        $response->setContent(json_encode($json));

        return $response;
    }

As suggested in:

https://github.com/genemu/GenemuFormBundle/blob/master/Resources/doc/jquery/autocomplete/entity_ajax.md

A different JSON structure is mentioned here but does not work at all for the autocompleter: http://stackoverflow.com/questions/22143219/want-to-use-genemu-formbundle-autocomplete-with-querybuilder

Generated Javascript:

jQuery(document).ready(function($) {
var $field = $('#integrator_contract_filter_branch');
var $autocompleter = $('#autocompleter_integrator_contract_filter_branch');
var $configs = {
focus: function(event, ui) {
return false;
},
select: function(event, ui) {
this.value = ui.item.label;
terms = ui.item;
$field.val(JSON.stringify(terms));
return false;
}
};
$configs.source = function(request, response) {
$.getJSON('/branch/ajax', {
term: request.term
}, response);
};
$autocompleter.autocomplete($configs);
});

When I select an entity my hidden input gets populated with the JSON array:

                <label for="integrator_contract_filter_branch" class="required">Branch</label><input value="{&quot;label&quot;:&quot;Foo (Bar)&quot;,&quot;value&quot;:2}" id="integrator_contract_filter_branch" name="integrator_contract_filter[branch]" required="required" type="hidden"><span class="ui-helper-hidden-accessible" aria-live="polite" role="status">2</span><input autocomplete="off" class="ui-autocomplete-input" id="autocompleter_integrator_contract_filter_branch" name="autocompleter_integrator_contract_filter[branch]" required="required" type="text">

Shouldn't the javasript function populate the hidden input with the ID by default?

Possibly related:

genemu / GenemuFormBundle

genemu_jqueryautocompleter_entity with AJAX route_name setting JSON as value #403