title: Where trigger the "Please enter a valid date." in jquery.validate.js
body: <p>I am using jQuery UI version 1.12.1 and jQuery Validation v1.15.0</p>
  
  <p>I created a datepicker as follow:</p>
  
  <pre><code>if ($.fn.datepicker) $(':input.date').datepicker({
            changeMonth: true,
            changeYear: true
      });
  </code></pre>
  
  <p>By default, the date format will be mm/dd/yyyy, for example 01/26/2017, represent 26th January 2017.</p>
  
  <p>I am trying to change the date format to be dd/mm/yyyy, so I change the datepicker as follow:</p>
  
  <pre><code>if ($.fn.datepicker) $(':input.date').datepicker({
        changeMonth: true,
        changeYear: true,
        dateFormat: 'dd/mm/yy'
  });
  </code></pre>
  
  <p>Well, now the date format display correct as I wish, it become 26/01/2017, represent 26th January 2017.</p>
  
  <p>However, it throw a red error message <code>Please enter a valid date.</code>. After my debugging, I found that the error message is actually come from the jquery.validate.js at line 357:</p>
  
  <pre><code>messages: {
          // some other code
          date: "Please enter a valid date.",
          // some other code
      },
  </code></pre>
  
  <p>Any idea how/why it throw this error message?</p>
  
  <p>Is it my jQuery UI version not compatible with the jQuery validation version?</p>
  
  <p>kindly advise.</p>