Problem with layout using update panels

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ASP.NET

UpdatePanel

I am implementing general layout using asp.net. This application uses single ASPX with dynamically loaded ASCX's:

<div class="page-all">
		<div id="page-left" class="page-left">
			<asp:UpdatePanel ID="UpdatePanel3" runat="server" UpdateMode="Conditional">
				<ContentTemplate>
					<div runat="server">
					</div>
				</ContentTemplate>
			</asp:UpdatePanel>
		</div>
		<div id="page-middle" class="page-middle">
			<asp:UpdatePanel ID="upContent" runat="server" UpdateMode="Conditional">
				<ContentTemplate>
					<div runat="server">
					</div>
				</ContentTemplate>
			</asp:UpdatePanel>
		</div>
		<div id="page-right" class="page-right">
			<asp:UpdatePanel ID="UpdatePanel2" runat="server" UpdateMode="Conditional">
				<ContentTemplate>
					<div runat="server">
					</div>
				</ContentTemplate>
			</asp:UpdatePanel>
		</div>
	</div>

In those inner divs I am loading ASCX using:

divContentPlaceholder.Controls.Add(LoadControl("~/Modules/Contents/test.ascx"));
upContent.Update();

One of those ASCX contains <asp:Button>. After clicking this button the hosting divs gets empty (ASCX is unloaded). Why i that? It does not even enter onclick handler in codebehind.

Thank you in advance for help