iTextSharp RadioCheckField.CheckType property problem

Question

For some reason when I set the CheckType property on the RadioCheckField object, it remains as the default (TYPE_CHECK). Does anyone know why this is happening?

        RadioCheckField bt2 = new RadioCheckField(stamp.Writer, new Rectangle(50, 50, 50, 50), "radio", "North");
        bt2.CheckType = RadioCheckField.TYPE_STAR;
        bt2.Checked = false;
        PdfFormField f3 = bt2.CheckField;