C# สงสัย...ทำไม Debug ปุ่ม submit มันวิ่งเข้าเงื่่อนไข (!Page.IsPostBack)

public partial class _Default : System.Web.UI.Page
    {
        SqlConnection objConn = new SqlConnection();
        SqlCommand objCmd = new SqlCommand();
        String strConnString = "--------------";
        String strSQL,Texture;
        protected void Page_Load(object sender, EventArgs e) 
        {
            objConn.ConnectionString = strConnString;
            objConn.Close();
            objConn.Open();
            if (!Page.IsPostBack)
            {
                ViewData();
            }
        }
        void ViewData(){
            SqlDataAdapter dtAdapter = new SqlDataAdapter("---------", objConn);
            dtAdapter.SelectCommand.Parameters.AddWithValue("-----------");
            //Data Table
            DataTable dt = new DataTable();
            dtAdapter.Fill(dt);
            if (dt.Rows.Count > 0)
            {
               .
               .
               .
            }          
        }
        void Page_Unload() {
            objConn.Close();
            objConn = null;
        }
        protected void SearchBtn_Click(object sender, EventArgs e)
        {
            this.pnlForm.Visible = true;
            ViewData();          
        }
        protected void btnSave_Click(object sender, EventArgs e)
        {          
                if (ID == "")
                {
                    this.lblCheck.Visible = true;
                    this.lblCheck.Text = "* Records require an new ID";
                }
                else
                {
                    objConn.ConnectionString = strConnString;
                    objConn.Open();
                    strSQL = "UPDATE Record SET Material = '" + Texture + "' " +
                            "WHERE [RecordID] = '" + this.txtRecID.Text + "' ";
                    objCmd = new SqlCommand();
                    objCmd.Connection = objConn;
                    objCmd.CommandText = strSQL;
                    objCmd.CommandType = CommandType.Text;
                    try
                    {
                        objCmd.ExecuteNonQuery();
                        objConn.Close();
                        this.lblCheck.Text = "* Record Inserted";
                        this.lblCheck.Visible = true;
                    }
                    catch (Exception ex)
                    {
                        objConn.Close();
                        this.lblCheck.Visible = true;
                        this.lblCheck.Text = "* Record can not insert Error (" + ex.Message + ")";
                    }
                }
        }