knockout foreach bug

HTML

<script src="http://ajax.aspnetcdn.com/ajax/knockout/knockout-2.1.0.js"></script>
<a href="javascript:;" data-bind="click: repopulate">Change items</a>
<ul>
    <!-- ko foreach: items -->                                                 
        <!-- ko template: { name: 'product_template'} -->
        <!-- /ko -->  
   <!-- /ko -->
</ul>

<ul>
    <li data-bind="template: { foreach: items, name: 'product_template' }"></li>
</ul>


<br />
<div data-bind="text: ko.toJSON($data)"></div>


<script type="text/html" id="product_template">
    <li data-bind="text: $data"></li>
</script>

CSS

ul li {float:left; padding-right:10px;}
ul {clear:both;}
span {color:red;}

JavaScript

function BrowseModel() {
    var self = this;
    self.items = ko.observableArray();
    self.itemsStep = ko.observable(1);
    self.repopulate = function() {
        self.itemsStep(self.itemsStep() + 3);
        return false;
    };
    ko.computed(function() {
        var arr = [];
        for (var i = self.itemsStep(); i <= self.itemsStep() + 5; i++) {
            arr.push(i);
        }
        self.items(arr);
    }, self);
}

ko.applyBindings(new BrowseModel());