title: Jquery can't check checkbox
body: <p>Refer to this fiddle:</p>
  
  <p><a href="http://jsfiddle.net/FwSF3/" rel="nofollow">http://jsfiddle.net/FwSF3/</a></p>
  
  <p><strong>HTML:</strong></p>
  
  <pre><code>&lt;input type="password" id="Password" tabindex="2"&gt;
  &lt;input id="PasswordChk" type="checkbox" disabled="disabled"/&gt;
  </code></pre>
  
  <p><strong>JS:</strong></p>
  
  <pre><code>$('#Password').on("keyup", function () {
      var password = $.trim($(this).val());    
      if(password.length == 0){
          $('#PasswordChk').removeAttr("checked");
      }else{
          $('#PasswordChk').attr("checked", "checked");
      }    
  });
  </code></pre>
  
  <p>When I first type into the textbox, the checkbox is set.  When I remove the text (length = 0) it's unchecked.</p>
  
  <p>However after unchecking, it can't re-check the checbox.</p>
  
  <p>Anyone know how to get around this?</p>