Why dynamically created user controls disappear when controls are not doing full postbacks?

Based on my current understandings, when you have an UpdatePanel control there is no full postback. Therefore if I dynamically add custom user controls and they have UpdatePanels that are updated in their code they shouldnt disappear from the page they are loaded into, right? Apparently not. I made a simple project to test and still my dynamic controls disappear when clicked even though they should not be triggering a full postback. I have an aspx page that loads the controls:

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="TESTmultipleScriptManagerControls.aspx.cs" Inherits="myPlayground.TESTmultipleScriptManagerControls" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<div>

    <asp:ScriptManager ID="ScriptManager1" runat="server">
    </asp:ScriptManager>

    <asp:UpdatePanel ID="UpdatePanel1" runat="server">
    <ContentTemplate>
    <asp:Button ID="Button1" runat="server" Text="Button" onclick="Button1_Click" />

    <asp:PlaceHolder ID="PlaceHolder1" runat="server"></asp:PlaceHolder>
    </ContentTemplate>
    </asp:UpdatePanel>

</div>
</form>
</body>
</html>

With the following code behind:

protected void Button1_Click(object sender, EventArgs e)
    {

        TESTcontrol1 temp = LoadControl("TESTcontrol1.ascx") as TESTcontrol1;
        PlaceHolder1.Controls.Add(temp);
        TESTcontrol1 temp2 = LoadControl("TESTcontrol1.ascx") as TESTcontrol1;
        PlaceHolder1.Controls.Add(temp2);

    }

And a simple user control:

<%@ Control Language="C#" AutoEventWireup="true" CodeBehind="TESTcontrol1.ascx.cs" Inherits="myPlayground.TESTcontrol1" %>
<asp:ScriptManagerProxy ID="ScriptManagerProxy1" runat="server">
</asp:ScriptManagerProxy>
<asp:UpdatePanel ID="UpdatePanel1" runat="server">

<ContentTemplate>
<asp:Button ID="Button1" runat="server" Text="Button" onclick="Button1_Click" />
<asp:Label ID="Label1" runat="server" Text="Label"></asp:Label>
</ContentTemplate>
</asp:UpdatePanel>

With the following code behind:

protected void Button1_Click(object sender, EventArgs e)
    {
        Label1.Text = System.DateTime.Now.ToString();
    }

Any ideas on why the controls are disappearing even though there shouldnt be a postback triggering?

Solution

OK based on my current understandings, when you have an UpdatePanel control there is no full postback.

Postbacks triggered from UpdatePanels always execute the full page life-cycle. All the events are triggered normally. It makes no difference whether you use an UpdatePanel or not. Every time you add a control programmatically you need to re-add it on every postback.

Read this post, it may help you understand a bit better what's going on here.