cssStickyHeaders and Bootstrap Buttons

HTML

<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/js/bootstrap.min.js"></script>
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/css/bootstrap.min.css">
<script src="https://rawgit.com/Mottie/tablesorter/master/dist/js/jquery.tablesorter.combined.min.js"></script>
<script src="https://rawgit.com/Mottie/tablesorter/master/dist/js/widgets/widget-math.min.js"></script>
<script src="https://rawgit.com/Mottie/tablesorter/master/dist/js/widgets/widget-cssStickyHeaders.min.js"></script>
<table id="table1" class="tablesorter">
  <thead>
    <tr>
      <th>Foo</th>
      <th>Bar</th>
    </tr>
  </thead>
  <tfoot>
    <tr>
      <th data-math="col-sum">col-sum</th>
      <th data-math="col-sum">col-sum</th>
    </tr>
  </tfoot>

  <tbody>

  </tbody>

</table>

CSS

.tablesorter thead tr {
  background-color: #444 !important;
  color: #ddd !important;
}

.tablesorter thead {
}

.tablesorter tbody .btn span.glyphicon {

}

JavaScript

$(function() {

  $('#table1').tablesorter({
    // delayInit: true,
    // debug: true,
    theme: 'bootstrap',
    widgets: [
      'zebra',
      'filter',
      'math',
      'cssStickyHeaders',
      'uitheme'
    ],
    widgetOptions: {
      filter_cssFilter: 'form-control',
      filter_reset: 'btn btn-xs',
      cssStickyHeaders_filteredToTop: false
    }
  });

  var icons = ['tower', 'stats', 'knight', 'lamp', 'ruble'];

  function updateData() {
    var $tblBody = $("#table1 tbody");
    $tblBody.empty();

    for (var i = 0; i < 66; ++i) {

      var btnStr = '';

      for (var j = 0; j < 9; ++j) {
        btnStr += '<span class="btn btn-primary btn-xs"><span class="glyphicon glyphicon-' +
          icons[Math.floor(Math.random() * icons.length)] + '" aria-hidden="true"></span></span>';
      }

      $("<tr></tr>")
        .append('<td>' + i + '</td><td>' + btnStr + '</td>')
        .appendTo($tblBody);
    }

    $("#table1").trigger("update");
  }

  updateData();
});