Slow databinding of a empty datatable

stopWatch = new Stopwatch();
stopWatch.Start();

// Create a datatable for the header with empty strings
DataTable header = new DataTable("FilterRow");

// Add all columns of the datasource to it
foreach (DataColumn col in _AllData.Columns)
{
    header.Columns.Add(new DataColumn(col.ColumnName, typeof(string)));
}

stopWatch.Stop();
TimeSpan s3 = stopWatch.Elapsed; // ===> 0.0966
stopWatch = new Stopwatch();
stopWatch.Start();

// Create a empty row for it
DataRow filterrow = header.NewRow();

foreach (FilterColumnClass filter in _FilterColumns) // While testing the timings this contained 80 columns
{
    if (filter.FilterCheckControl.Visible)
    {
        try
        {
            filterrow.ItemArray[filter.Index] = filter.FilterTextString; // While testing the timings all these variables where empty
        }
        catch (Exception ex)
        {
            PublicFunctions.ReportBug(ex, _Shared);
        }
    }
}

// Add the filter row to the header datatable
header.Rows.Add(filterrow);

stopWatch.Stop();
TimeSpan s4 = stopWatch.Elapsed; // ===> 0.1811 ms
stopWatch = new Stopwatch();
stopWatch.Start();

// Assign the header datatable to the grid
gridHeader.DataSource = header;

stopWatch.Stop();
TimeSpan s5 = stopWatch.Elapsed;  // ===> 165.3965 ms WHY??????

MessageBox.Show(
    "PrepareFilterColumns" + Environment.NewLine +
    "#1-2#: " + s1.TotalMilliseconds.ToString() + Environment.NewLine +
    "#2-3#: " + s2.TotalMilliseconds.ToString() + Environment.NewLine +
    "#3-4#: " + s3.TotalMilliseconds.ToString() + Environment.NewLine +
    "#4-5#: " + s4.TotalMilliseconds.ToString() + Environment.NewLine +
    "#5-6#: " + s5.TotalMilliseconds.ToString() + Environment.NewLine);