title: Why does jQuery datapicker not constrain input when setting a date format?
body: <p>I have an input field that is being set as a date picker. When I initialize the dateFormat option it stops constraining the input and I can enter all sorts of rubbish dates in the text box. Why does this happen? I'd like to have constrained input still work when setting a custom date format.</p>
  
  <pre><code>myTextInput.datepicker({ dateFormat: "dd-M-yy" });
  </code></pre>
  
  <p>If I don't set the dateFormat option then the input is constrained as expected.</p>