Header checkbox doesn't fire event with AW.Grid.Extended

I want a checkbox in a header like you have in your example:


<script type="text/javascript">

var checkbox = new AW.UI.Checkbox;
checkbox.setControlText("checkbox");
checkbox.setControlValue(true);

var grid1 = new AW.UI.Grid;
grid1.setId("grid1");
grid1.setHeaderTemplate(checkbox, 0);
grid1.setHeaderText("header");
grid1.setCellText("cell");
grid1.setColumnCount(4);
grid1.setRowCount(5);
grid1.refresh();

checkbox.onControlValueChanged = function(value){
grid1.setCellText(value, 0, 0);
}
</script>



This works fine. However if I change the line: var grid1 = new AW.UI.Grid;

To be var grid1 = new AW.Grid.Extended;

Then the code breaks - no event seems to be triggered on the click of the checkbox.

Please help.