Drop down on selectedindexchanged, always take first value

I created a drop down
populated it dynamically
write a code to display some value based on selectedindexchanged event

but it always takes the first value.


pls help me

code
-------------------------------------------------
// Page Load
  protected void Page_Load( object sender, EventArgs e )
    {
      

       if (!IsPostBack)
        {
           PopulateMultipleAddress();
        }
    }
------------------------------------------------ loading dropdown, it is postback
private void PopulateMultipleAddress()
     {

      int cid = 0 ;
      cid = Convert.ToInt32(DataAccessContext.CustomerRepository.GetIDFromUserName(Membership.GetUser().UserName));

      MemberAddress ma = new MemberAddress();
      DataSet ds = ma.MemberAddressListing(cid);

      if (ds.Tables[0].Rows.Count == 0)
       {
         uxShippingSelectAddress.Text = "No Multiple Address Found!";
       }
      else
       {
         uxShippingSelectAddress.DataSource = ds.Tables[0];
         uxShippingSelectAddress.DataTextField = ds.Tables[0].Columns["Address1"].ColumnName.ToString();
         uxShippingSelectAddress.DataValueField = ds.Tables[0].Columns["RowID"].ColumnName.ToString();
         uxShippingSelectAddress.DataBind();
         uxShippingSelectAddress.Items.Insert(0, new ListItem("Select your shipping address"));
         uxShippingSelectAddress.SelectedIndex = 0;
       }

    }
---------------------------------------------- on dropdown selected index change
  protected void uxShippingSelectAddress_SelectedIndexChanged(object sender, EventArgs e)
    {
        PopulateShippingAddressesOnSelect(uxShippingSelectAddress.SelectedIndex);
     }
-------------------------------------------
 private void PopulateShippingAddressesOnSelect(int rid)
    {
        if (rid != 0)
        {
            MemberAddress ma = new MemberAddress();
            DataSet ds = ma.MemberAddressListingByRID(rid);
         
                uxShippingFirstName.Text = ds.Tables[0].Columns["FirstName"].ColumnName.ToString();
                uxShippingLastName.Text = ds.Tables[0].Columns["LastName"].ColumnName.ToString();
                uxShippingCompany.Text = ds.Tables[0].Columns["Company"].ColumnName.ToString();
                uxShippingAddress1.Text = ds.Tables[0].Columns["Address1"].ColumnName.ToString();
                uxShippingAddress2.Text = ds.Tables[0].Columns["Address2"].ColumnName.ToString();
                uxShippingCity.Text = ds.Tables[0].Columns["City"].ColumnName.ToString();
                uxCountryState.CurrentState = ds.Tables[0].Columns["State"].ColumnName.ToString();
                uxShippingZip.Text = ds.Tables[0].Columns["Zip"].ColumnName.ToString();
                uxCountryState.CurrentCountry = ds.Tables[0].Columns["Country"].ColumnName.ToString();
                uxShippingPhone.Text = ds.Tables[0].Columns["Phone"].ColumnName.ToString();
                uxShippingFax.Text = ds.Tables[0].Columns["Fax"].ColumnName.ToString();
           
        }
    }