Polymer 1.0 test for nested templates

HTML

<script src="https://elements.polymer-project.org/bower_components/webcomponentsjs/webcomponents-lite.js"></script>
<script src="https://cdn.rawgit.com/download/polymer-cdn/1.1.4/lib/polymer/polymer.html"></script>

<!--<script src="https://cdn.rawgit.com/download/polymer-cdn/1.1.4/lib/webcomponentsjs/webcomponents-lite.js"></script>-->

<link rel="import" href="https://cdn.rawgit.com/download/polymer-cdn/1.1.4/lib/paper-button/paper-button.html" />
<link rel="import" href="https://cdn.rawgit.com/download/polymer-cdn/1.1.4/lib/paper-checkbox/paper-checkbox.html" />

    
<dom-module is="wc-rnd-checkboxes">
    <template>
        <paper-button on-click="handleRndGenerator">Random Items</paper-button><br />
        
        <template is="dom-repeat" items="{{data}}">
            <paper-checkbox></paper-checkbox>
            <span>{{index}}</span>
            <br />
        </template>
        
    </template>
</dom-module>

 <h3>Polymer Dom-repeat and paper-checkbox</h3>

<p>
    <b>Instructions:</b> 
    <ol>
        <li>click on the first checkbox;</li>  
        <li>click on generate "Random Items";</li>  
        <li>Issue: Polymer does not uncheck the first checkbox</li>
    </ol>
</p>
<wc-rnd-checkboxes></wc-rnd-checkboxes>

JavaScript

Polymer({
     is: "wc-rnd-checkboxes",
     properties: {
         data: { type: Array, value: [1, 2, 3, 4, 5] }
     },

     handleRndGenerator: function() {
         this.data = [];
         var length = Math.floor((Math.random() * 5) + 0)
         for (i=0; i < length; i++) {

             var irnd = Math.floor((Math.random() * 10) + 1);
             this.data.push(irnd);
         }

     }
 });