Asp.net: conditional loading of user controls fails

Hello (sorry for the poor title)

I have a user control which loads different additional user controls based on some conditions like this:

<%@ Control Language="C#" AutoEventWireup="true" CodeFile="SubPage.ascx.cs" Inherits="SubPage" %>
<%@ Register Src="<srcA>" TagName="A" TagPrefix="CTRL" %>
<%@ Register Src=">srcB>" TagName="B" TagPrefix="CTRL" %>

<% if (someValue == 1) { %>
    Loading user control A..
    <CTRL:A runat="server" />
<% } else { %>
    Loading user control B..
    <CTRL:B runat="server" />
<% } %>

The result will look correct; the expected content is displayed. But I noticed that even though someValue != 1 and control B is displayed, control A is still loaded behind the scenes (page load is called).

Why is this? And what would be a better approach? Thanks.