ASP.NET ใช้ Datagrid แล้วทํา Paging ของ Datagrid แต่กดย้อนกลับ แล้วมันจะ Next page ตลอด

private void Bind_GV_Stock_Movement()
    {
        string sql = "SELECT CASE WHEN App.stock_card.is_recv = 1 THEN 'รับ' ELSE 'จ่าย' END AS status, qty_entry, qty_out, total, comment, datetime FROM App.stock_card";
        cmd = conn.CreateCommand();
        cmd.CommandType = CommandType.Text;
        cmd.CommandText = sql;
        cmd.ExecuteNonQuery();
        dp = new SqlDataAdapter(cmd);
        dp.Fill(dt);

        GV_Stock_Movement.DataSource = dt;
        GV_Stock_Movement.DataBind();
    }

    protected void GV_Stock_Movement_PageIndexChanging(object sender, GridViewPageEventArgs e)
    {
        string sql = "SELECT CASE WHEN App.stock_card.is_recv = 1 THEN 'รับ' ELSE 'จ่าย' END AS status, qty_entry, qty_out, total, comment, datetime FROM App.stock_card";
        cmd = conn.CreateCommand();
        cmd.CommandType = CommandType.Text;
        cmd.CommandText = sql;
        cmd.ExecuteNonQuery();
        dp = new SqlDataAdapter(cmd);
        dp.Fill(dt);

        GV_Stock_Movement.DataSource = dt;
        GV_Stock_Movement.PageIndex = e.NewPageIndex;
        GV_Stock_Movement.DataBind();
    }