Use optgroup with knockout.js

I'm trying to manually display options inside optgroups in knockout.js, with guidance from Ryan Niemeyer's answer here . It works great, but only if the options are displayed immediately. If they are loaded subsequently, the correct item will not be selected.

Below is the code and script. Change

t: ko.observable(null)

      

        
        
        
      

    

to

t: ko.observable(t)

      

        
        
        
      

    

makes it work, so the issue is definitely load latency and I have ValueAllowUnset set to true.

script: http://jsfiddle.net/exyy7hq2/3/

Html

<select data-bind="template: { name: 'selectTemplateType', data: t }, valueAllowUnset: true, value: selectedId"></select>
<div data-bind='text: selectedId'></div>

<script type="text/html" id="selectTemplateType">
    <!-- ko ifnot: $data -->
        <option>No template selected</option>
    <!-- /ko -->
    <!-- ko if: $data -->
        <option>Select</option>
        <!-- ko foreach: groups -->
            <optgroup data-bind="attr: { 'label': name }, foreach: types">
                <option data-bind="option: id, text: name"></option>
            </optgroup>
        <!-- /ko -->
    <!-- /ko -->
</script>

      

        
        
        
      

    

JavaScript

ko.bindingHandlers.option = {
    update: function(element, valueAccessor) {
       var value = ko.utils.unwrapObservable(valueAccessor());
       ko.selectExtensions.writeValue(element, value);   
    }        
};

var t = {
    groups: [
        { name: 'a', types: [{id: 1, name: 't1'}] },
        { name: 'b', types: [{id: 102, name: 't2'}, {id: 103, name: 't3'}] },
        { name: 'c', types: [{id: 5, name: 'x'}] }
    ]
}
var vm = {
    t: ko.observable(null),
    selectedId: ko.observable(103)
};
ko.applyBindings(vm);
setTimeout(function(){ vm.t(t); }, 2000);