Colvis error when using headerCallback to change col headings

I just upgraded from dt 1.13 -> 2.1 and found that the colVis buttons crashes when changing the column headers.
My use-case is that I want to include the sum total in the col header and also use the colVis button feature.

<link href="https://cdn.datatables.net/v/bs/jszip-3.10.1/dt-2.1.8/b-3.2.0/b-colvis-3.2.0/b-html5-3.2.0/b-print-3.2.0/fc-5.0.4/fh-4.0.1/sl-2.1.0/datatables.min.css" rel="stylesheet" />
<script src="https://cdn.datatables.net/v/bs/jszip-3.10.1/dt-2.1.8/b-3.2.0/b-colvis-3.2.0/b-html5-3.2.0/b-print-3.2.0/fc-5.0.4/fh-4.0.1/sl-2.1.0/datatables.min.js"></script>

<script>
datatable = $('.datatableclass').DataTable( {
  "dom": "<'row'<'col-sm-3'l><'col-sm-4'i><'col-sm-5'f>>" +
  "<'row'<'col-sm-12'tr>>" +
  "<'row'<'col-sm-6'i><'col-sm-6'p>>",
  "ajax": { ... },
  buttons: [
    { extend: 'csvHtml5',
      text: 'Export Table',
      exportOptions: {columns: ':gt(0):visible'},
    },
    { extend: 'colvis',
      text: 'Columns',
      columns: [2,3,4, ':gt(5)']
    }
  ],
 "headerCallback": function( thead, data, start, end, display ) {
    var api = this.api();

    $( api.column( 11 ).header() ).html('Billed')); // Works if this line is removed.
},
...
</script>

<table class="table datatableclass">
</table>

The code is simplified here shows the problem, but this all worked using dt v1.13

Browser console shows the following error:

Uncaught TypeError: o is undefined
    _columnText https://cdn.datatables.net/v/bs/jszip-3.10.1/dt-2.1.8/b-3.2.0/b-colvis-3.2.0/b-html5-3.2.0/b-print-3.2.0/fc-5.0.4/fh-4.0.1/sl-2.1.0/datatables.min.js:51
    text https://cdn.datatables.net/v/bs/jszip-3.10.1/dt-2.1.8/b-3.2.0/b-colvis-3.2.0/b-html5-3.2.0/b-print-3.2.0/fc-5.0.4/fh-4.0.1/sl-2.1.0/datatables.min.js:51
    i https://cdn.datatables.net/v/bs/jszip-3.10.1/dt-2.1.8/b-3.2.0/b-colvis-3.2.0/b-html5-3.2.0/b-print-3.2.0/fc-5.0.4/fh-4.0.1/sl-2.1.0/datatables.min.js:40
    _buildButton https://cdn.datatables.net/v/bs/jszip-3.10.1/dt-2.1.8/b-3.2.0/b-colvis-3.2.0/b-html5-3.2.0/b-print-3.2.0/fc-5.0.4/fh-4.0.1/sl-2.1.0/datatables.min.js:40
    _expandButton https://cdn.datatables.net/v/bs/jszip-3.10.1/dt-2.1.8/b-3.2.0/b-colvis-3.2.0/b-html5-3.2.0/b-print-3.2.0/fc-5.0.4/fh-4.0.1/sl-2.1.0/datatables.min.js:40
    _expandButton https://cdn.datatables.net/v/bs/jszip-3.10.1/dt-2.1.8/b-3.2.0/b-colvis-3.2.0/b-html5-3.2.0/b-print-3.2.0/fc-5.0.4/fh-4.0.1/sl-2.1.0/datatables.min.js:40
    _expandButton https://cdn.datatables.net/v/bs/jszip-3.10.1/dt-2.1.8/b-3.2.0/b-colvis-3.2.0/b-html5-3.2.0/b-print-3.2.0/fc-5.0.4/fh-4.0.1/sl-2.1.0/datatables.min.js:40
    add https://cdn.datatables.net/v/bs/jszip-3.10.1/dt-2.1.8/b-3.2.0/b-colvis-3.2.0/b-html5-3.2.0/b-print-3.2.0/fc-5.0.4/fh-4.0.1/sl-2.1.0/datatables.min.js:40
    _constructor https://cdn.datatables.net/v/bs/jszip-3.10.1/dt-2.1.8/b-3.2.0/b-colvis-3.2.0/b-html5-3.2.0/b-print-3.2.0/fc-5.0.4/fh-4.0.1/sl-2.1.0/datatables.min.js:40
    A https://cdn.datatables.net/v/bs/jszip-3.10.1/dt-2.1.8/b-3.2.0/b-colvis-3.2.0/b-html5-3.2.0/b-print-3.2.0/fc-5.0.4/fh-4.0.1/sl-2.1.0/datatables.min.js:40
    <anonymous> https://cdn.datatables.net/v/bs/jszip-3.10.1/dt-2.1.8/b-3.2.0/b-colvis-3.2.0/b-html5-3.2.0/b-print-3.2.0/fc-5.0.4/fh-4.0.1/sl-2.1.0/datatables.min.js:40
    jQuery 7
...