dynamic control event

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ASP.NET

if (dt1.Rows.Count > 0)
{
  for (int i = 0; i < dt1.Rows.Count; i++)
  {
     Panel pnlTextBox= new Panel();
     pnlTextBox.ID = "pnlTextBox_" + i.ToString();
     pnlTextBox.CssClass = "tagpanel";
     TextBox txt = new TextBox();                //Textbox
     txt.ID = "txt_" + i.ToString();
     txt.CssClass = "txtb";
     txt.AutoPostBack = true;
     txt.EnableViewState = true;
     txt.Text = dt1.Rows[i][5].ToString();
        
     if (dt1.Rows[i][1].ToString() == "1")
     {
        txt.Enabled = false;
     }
   
     txt.MaxLength = 8;
     txt.AutoPostBack = true;

     Button Btn = new Button();                 //Save Button
     Btn.ID = "Btn_" + i.ToString();
     Btn.Text = "Save";
     Btn.CssClass = "btnCss";
                   
     Btn.Click += new System.EventHandler(this.Btn_test);

     Literal ltbr1 = new Literal();              //new line 
     ltbr1.ID = "ltbr1" + i.ToString();
     ltbr1.Text = "<br />";

     Label lbl = new Label();                  //tag name
     lbl.ID = "lbl_" + i.ToString();
     lbl.CssClass = "lblCss";
     lbl.Text = dt1.Rows[i][0].ToString();

     Label TagId = new Label();              //tag id
     TagId.ID = "Tag_" + i.ToString();
     TagId.Text = dt1.Rows[0][6].ToString();
     TagId.Visible = false;

     Label OldValue = new Label();             //tag value...used to store old value
     OldValue.ID = "old_" + i.ToString();
     OldValue.Text = dt1.Rows[i][3].ToString();
     OldValue.Visible = false;

     pnlTextBox.Controls.Add(txt);
     //    pnlTextBox.Controls.Add(img);
     pnlTextBox.Controls.Add(ltbr1);
     pnlTextBox.Controls.Add(lbl);
     pnlTextBox.Controls.Add(TagId);
     pnlTextBox.Controls.Add(OldValue);
     if (dt1.Rows[i][1].ToString() == "1")
     {
         pn1.Controls.Add(pnlTextBox);
         //    pn1.Controls.Add(ltbr);
     }
     else
     {
         pnlTextBox.Controls.Add(Btn);
         pn2.Controls.Add(pnlTextBox);
         //  pn2.Controls.Add(ltbr); 
      }                  
   }
}

this is my Code to create dynamic control.I have call this function at page pre_init state. Button event is also worked properly. But i have one problem.When I am write new value in text box which is dynamically created causes page load. Why this is happennig??? Because of this when i am changing the value in textbox and if my focus is in textbox then click event of button not works.It will work after page load. why this is happening?? where should i went wrong??