title: Knockout.js: Initial value of observable doesn't update RadioButton state
body: <p>Here is a <strong>very simple</strong> story that I fail to make it work: </p>
  
  <p>We have an array of <code>questions</code>. Each question has an array of <code>answer</code>. Each answer has a <code>text</code> and <code>value</code>. Each <code>question</code> has the property <code>selectedAnswer</code> that represents the selected answer's <code>value</code>.</p>
  
  <p>Here is jsfiddle: <a href="https://jsfiddle.net/votsevfd/8/" rel="nofollow noreferrer">https://jsfiddle.net/votsevfd/8/</a></p>
  
  <p><strong>Implementation:</strong></p>
  
  <pre><code>&lt;div data-bind="foreach : {data: questions}"&gt;
  
  Question: &lt;span data-bind="text: descr"&gt;&lt;/span&gt;
  &lt;div data-bind="foreach: {data: answers}"&gt;
    &lt;div&gt;    
      &lt;label data-bind="text: text"&gt;&lt;/label&gt;
      &lt;input name="something" type="radio" data-bind="checked: $parent.selectedAnswer, value: value"&gt;&lt;/input&gt;    
    &lt;/div&gt;
  &lt;/div&gt;
  &lt;div&gt;
  The selected answer is:&lt;span data-bind="text: selectedAnswer"&gt;&lt;/span&gt;
  &lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>And here is the related <code>JavaScript</code>:</p>
  
  <pre><code> var model = {
    questions: ko.observableArray(),
    };
  
  var q1 = {
    descr: 'Do you like JS?',
    selectedAnswer: ko.observable('200'), // Initially, select No (200)
    answers: [
      {text:'Yes', value:'100'},
      {text:'No', value:'200'}
    ],
  }
  model.questions.push(q1);
  
  ko.applyBindings(model);
  </code></pre>
  
  <p><strong>Problem:</strong>
  I want the appropriate radio button become selected according to initial value of <code>selectedAnswer</code> (in the above case, radio button <code>No</code>). But it doesn't work.</p>
  
  <p>What am I missing?</p>