title: md-datepicker shows up red underline even though the date is valid
body: <pre><code>&lt;md-datepicker name="startDate"  md-is-error="data.isInvalid(Form.startDate)" ng-model="data.startDate" md-placeholder="Start date" required flex="100" flex-lg="50"&gt;&lt;/md-datepicker&gt;
  &lt;div ng-messages="Form.startDate.$error" ng-if="data.isInvalid(Form.startDate)"&gt;
      &lt;div ng-message="valid"&gt;The entered value is not a date!&lt;/div&gt;
      &lt;div ng-message="required"&gt;This date is required!&lt;/div&gt;
      &lt;div ng-message="mindate"&gt;Date is too early!&lt;/div&gt;
      &lt;div ng-message="maxdate"&gt;Date is too late!&lt;/div&gt;
  &lt;/div&gt;
  
  
  isInvalid : function(formObject) {
      return formObject.$invalid &amp;&amp; (formObject.$$parentForm.$submitted || formObject.$touched || formObject.$dirty);
  }
  </code></pre>
  
  <p>I am using md-datepicker. When I populate the data using the model I am getting an red line underneath the datepicker input box. the date is a valid one but I am not sure why its showing so. Please refer the screenshot attached for more reference. Did anyone face this issue ? Your suggestions are highly appreciated.
  <a href="https://i.stack.imgur.com/U1LNf.png" rel="noreferrer"><img src="https://i.stack.imgur.com/U1LNf.png" alt="enter image description here"></a></p>