title: ng-hide not working once the input field is clicked
body: <pre><code>    &lt;md-radio-group ng-model="orderDetails.productType" layout="row"&gt;
              &lt;md-radio-button value="paper" class="md-primary"&gt;&lt;h4&gt;Paper&lt;/h4&gt;&lt;/md-radio-button&gt;
              &lt;md-radio-button value="nonPaper"&gt;&lt;h4&gt;nonPaper&lt;/h4&gt;&lt;/md-radio-button&gt;
      &lt;/md-radio-group&gt;
  
  &lt;md-input-container class="md-block" ng-hide="orderDetails.productType === 'paper'" &gt;
      &lt;label&gt;Non-Paper Type&lt;/label&gt;
      &lt;input  type="text" name="nonPaperType" ng-required="orderDetails.productType === 'nonPaper'" ng-model="orderDetails.nonPaperType"/&gt;
  &lt;/md-input-container&gt;
  </code></pre>
  
  <p>I am trying to hide the input container, however, first it works fine, but after clicking on the input it won't hide.</p>
  
  <p><img src="https://i.stack.imgur.com/VWniT.png" alt="screenshot for issue"></p>