AJAX :: Text In Tabpanel Not Shown But Text Is Rendered To Browser

I have placed the code below on a page. The strange thing is that the "SOME TEXT" string doesnt show up in the page! I do see "upanel" and "pnl":

upanel
<asp:UpdatePanel ID="UpdatePanel2" runat="server">
<ContentTemplate>
pnl
<cc1:TabContainer OnActiveTabChanged="TabChanged" ID="tabContainer" runat="server"
ActiveTabIndex="0" OnClientActiveTabChanged="ActiveTabChanged" Width="100%">
<cc1:TabPanel ID="tp1" runat="server" HeaderText="A tab">
<ContentTemplate>
<asp:UpdatePanel ID="UpdatePanel3" runat="server" UpdateMode="Always">
<ContentTemplate>
SOME TEXT
</ContentTemplate>
</asp:UpdatePanel>
</ContentTemplate>
</cc1:TabPanel>
</cc1:TabContainer>
</ContentTemplate>
</asp:UpdatePanel>

HOWEVER, when I view the pagesource, I see this, so the text IS rendered to the browser! What can be happening here?

upanel
<div id="ctl00_CPHCenter_UpdatePanel2">
pnl
<div id="ctl00_CPHCenter_tabContainer" style="width:100%;visibility:hidden;">
<div id="ctl00_CPHCenter_tabContainer_header">
<span id="ctl00_CPHCenter_tabContainer_tp1_tab"><span><span><span id="__tab_ctl00_CPHCenter_tabContainer_tp1">A tab</span></span></span></span>
</div><div id="ctl00_CPHCenter_tabContainer_body">
<div id="ctl00_CPHCenter_tabContainer_tp1">
<div id="ctl00_CPHCenter_tabContainer_tp1_UpdatePanel3">
SOME TEXT
<div>
</div>