buttons disappearing from the parent table

mba_aslam

When expanding child record datatable from the parent table, the parent table buttons (Copy,Excel,Csv,Print) are disappearing

Here's my code

//parent table
var table=$('#datatable').DataTable({
"dom": 'lBtirp',
"ajax": { ...// code },
buttons: ['copyHtml5','excelHtml5','csvHtml5','print']
});

//child table
var subtable=$('table#'+subtable_id).DataTable({
"dom": 'ltirp',
"ajax": { ...// code },
...
});

// Add event listener for opening and closing details
$('#datatable tbody').on('click', 'td.details-control', function () {

  tr = $(this).closest('tr');
  var tdi = tr.find("i.fa");
  row = table.row( tr );

  if ( row.child.isShown() ) {
      // This row is already open - close it
      row.child.hide();
      tr.removeClass('shown');
      tdi.first().removeClass('fa-minus-square');
      tdi.first().addClass('fa-plus-square');
  }
  else {
      // Open this row
      //row.child( format(row.data()) ).show();
      request_id=row.data().request_id;
      response_id=row.data().response_id;

      var subtable_id = "subtable-"+request_id;
      row.child(format(subtable_id)).show();
      tr.addClass('shown');
      sub_DataTable(subtable_id, tr);
      tdi.first().removeClass('fa-plus-square');
      tdi.first().addClass('fa-minus-square');
  }

} );