tooltip for asp.net dropdownlist not Wroking

Tooltip for asp.net dropdownlist not Wroking for Select 2nd time Select.only Work 1st time Select.


This is My code

     protected void dropdownConsignee_DataBound(object sender, EventArgs e)
        {
       
                string CustomerName;
                DataSet Ds = new DataSet();
                String cusCode = txtCusCode.Text.Trim();
                Ds = BAL.HAWB_Outbound.conSigneeList(cusCode);


                int ItemCount = dropdownConsignee.Items.Count;
                for (int i = 0; i < ItemCount; i++)
                {
                    dropdownConsignee.Items[i].Attributes.Add("Title", Ds.Tables[0].Rows[i]["Address"].ToString());
                }
                dropdownConsignee.Items.Insert(0, new ListItem("Select", "Address"));
                dropdownConsignee.SelectedItem.Selected = false;
                dropdownConsignee.Items.FindByText("Select").Selected = true;


        }