I have a PopupControlExtender inside of the UpdatePanel. I use it to edit some of the values on the website.
Here is a code from Firebug - you can notice Panel1 and all the controls inside of it being generated 3 times when i load a page (once) and twice after two partial postbacks:
<form id="form1" action="Test.aspx" method="post" name="form1">
<input type="hidden" value=";;AjaxControlToolkit, Version=3.0.30930.21526, Culture=neutral, PublicKeyToken=28f01b0e84b6d53e:pl-PL:c83bc095-c5d9-40da-b175-dc46338fcc3a:865923e8:91bd373d:596d588c:411fea1c:e7c87f07:bbfda34c:30a78ec5:42b7c466;" id="ToolkitScriptManager1_HiddenField" name="ToolkitScriptManager1_HiddenField">
var theForm = document.forms['form1'];
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