When the panel size get bigger in c#, it Malfunction

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C#

I have the below code to add the textbox to the panel dynamically:

{
      TextBox[] textbox_item_array = new TextBox[6]; item_textbox.Add(textbox_item_array);
      textbox_item_array[0] = new TextBox();
      textbox_item_array[0].Width = label_bill_item_code.Width;
      textbox_item_array[0].Height = 26;
      textbox_item_array[0].Font = print_font_default;
      textbox_item_array[0].Location = new Point(label_bill_item_code.Location.X, 45 + (20 * row_count));
      textbox_item_array[0].Name = string.Concat("item_code", row_count.ToString());
      panel_bill_item_collections.Controls.Add(textbox_item_array[0]);
      textbox_item_array[0].KeyDown += new KeyEventHandler(dynamic_textbox_keydown);
      textbox_item_array[0].Leave += new EventHandler(dynamic_text_item_code_Leave);
      textbox_item_array[0].DoubleClick += new EventHandler(bill_new_Form_DoubleClick);
      textbox_item_array[1] = new TextBox();
      textbox_item_array[1].Width = label_bill_item_details.Width;
      textbox_item_array[1].Font = textbox_item_array[0].Font;
      textbox_item_array[1].Location = new Point(label_bill_item_details.Location.X, textbox_item_array[0].Location.Y);
      textbox_item_array[1].Name = string.Concat("item_description", row_count.ToString());
      textbox_item_array[1].KeyDown += new KeyEventHandler(dynamic_textbox_keydown);
      panel_bill_item_collections.Controls.Add(textbox_item_array[1]);
      textbox_item_array[2] = new TextBox();
      textbox_item_array[2].Width = label_bill_item_unit.Width;
      textbox_item_array[2].Font = textbox_item_array[0].Font;
      textbox_item_array[2].Location = new Point(label_bill_item_unit.Location.X, textbox_item_array[0].Location.Y);
      textbox_item_array[2].Name = string.Concat("item_unit", row_count.ToString());
      textbox_item_array[2].KeyDown += new KeyEventHandler(dynamic_textbox_keydown);
      panel_bill_item_collections.Controls.Add(textbox_item_array[2]);
      textbox_item_array[3] = new TextBox();
      textbox_item_array[3].Width = label_bill_item_price.Width;
      textbox_item_array[3].Font = textbox_item_array[0].Font;
      textbox_item_array[3].Location = new Point(label_bill_item_price.Location.X, textbox_item_array[0].Location.Y);
      textbox_item_array[3].Name = string.Concat("item_price", row_count.ToString());
      textbox_item_array[3].KeyDown += new KeyEventHandler(dynamic_textbox_keydown);
      panel_bill_item_collections.Controls.Add(textbox_item_array[3]);
      textbox_item_array[4] = new TextBox();
      textbox_item_array[4].Width = label_bill_item_quantity.Width;
      textbox_item_array[4].Font = textbox_item_array[0].Font;
      textbox_item_array[4].Location = new Point(label_bill_item_quantity.Location.X, textbox_item_array[0].Location.Y);
      textbox_item_array[4].Name = string.Concat("item_quantity", row_count.ToString());
      textbox_item_array[4].KeyDown += new KeyEventHandler(dynamic_textbox_keydown);
      textbox_item_array[4].Leave += new EventHandler(bill_new_Form_Leave);
      panel_bill_item_collections.Controls.Add(textbox_item_array[4]);
      textbox_item_array[5] = new TextBox();
      textbox_item_array[5].Width = label_bill_item_total.Width;
      textbox_item_array[5].Font = textbox_item_array[0].Font;
      textbox_item_array[5].Location = new Point(label_bill_item_total.Location.X, textbox_item_array[0].Location.Y);
      textbox_item_array[5].Name = string.Concat("item_total", row_count.ToString());
      textbox_item_array[5].KeyDown += new KeyEventHandler(dynamic_textbox_keydown);
      panel_bill_item_collections.Controls.Add(textbox_item_array[5]);
      row_count++;
      textbox_item_array[0].Focus();
  }

The code works fine while the size of the panel is not changed but if the size get changed, the panel Malfunction. What I can see is that if I increase the size of the panel it works fine till it approaches its size then it has problem again after it get bigger. Can you please help me with this problem? If the panel is not appropriate for this use, can you guide me which container is fine.