title: jqueryui autocomplete with a header in prepend giving null reference when scrolling with keyboard
body: <p>I'm using jquery 1.11.1 and jqueryui 1.11.2.  The problem is appearing in windows 8.1 running IE.  The autocomplete uses "open" to prepend a header into the result set.  when you arrow down the first arrow down click will result in a "unable to get property 'value' of undefined or null reference.</p>
  
  <p>So here is part of the autocomplete</p>
  
  <pre><code> open: cComboboxOpenApplica,
   focus: function (event, ui) {//what populates the drop down
          $("[id$=txtApplicant]").val(ui.item.label);
          $("[id$=hfApplicantID]").val(ui.item.value);
  
          return false;
      },
  </code></pre>
  
  <p>and the function that is called by the open</p>
  
  <pre><code>function cComboboxOpenApplicant(event) {
  
  var mComboboxOpenApplicant = '&lt;li style="font-size:10px; padding-left:5px; padding-bottom:20px"&gt;&lt;div class="divUIMultiColumnHeader" style="width:100px"&gt;First Name&lt;/div&gt;&lt;div class="divUIMultiColumnHeader" style="width:150px"&gt;Last Name&lt;/div&gt;&lt;div class="divUIMultiColumnHeader" style="width:50px"&gt;SSN&lt;/div&gt;&lt;div class="divUIMultiColumnHeader" style="width:100px"&gt;ID&lt;/div&gt;&lt;/li&gt;&lt;/a&gt;';
  $("ul.ui-autocomplete").prepend(mComboboxOpenApplicant);
  </code></pre>
  
  <p>}</p>
  
  <p>Again, this all works when I use the mouse.  When using the mouse if you mouse over the header row at the top of the returned results it does not hightlight that first line and does not allow you to click on it either.  If you use the keyboard and hit the down arrow once you get the error because it's trying to hightlight that first line that has the header in it and errors on </p>
  
  <pre><code>  focus: function (event, ui) {//what populates the drop down
          $("[id$=txtApplicant]").val(ui.item.label);
          $("[id$=hfApplicantID]").val(ui.item.value);
  
          return false;
      },
  </code></pre>
  
  <p>in the line ui.item.label</p>
  
  <p>What am I missing to help with this issue.</p>