I have the same issue. But because or markup is more complex than posted here by other users, I'll provide you this informations so that you can take care of when resolving the problems. I cannot provide you a complete example because we use lots of custom and user controls (which mostly inherit from ASP.NET or ATLAS-Controls) but will show you some simplified markup to give you an idea of what control hierarchy we have:
<asp:Panel>
<asp:TreeView></asp:TreeView><%-- some other stuff --%>
<atlas:UpdatePanel>
<ContentTemplate>
<asp:CheckBox/>
<atlasToolkit:ToggleButton/> <%-- for the CheckBox. We have two Checkboxes with relating ToggleButtonExtenders --%>
</ContentTemplate>
</atlas:UpdatePanel>
<asp:MultiView>
<asp:View>
<%-- Here is a DataGrid and some simple Controls --%>
</asp:View>
<asp:View>
<atlas:UpdatePanel>
<ContentTemplate>
<asp:Image> <%-- This is a big detailed image --%>
<asp:Panel>
<%-- Some simple Controls: Buttons, Labels etc. which are needed for the CollapsiblePanelExtender --%>
<asp:Image> <%-- Overview image for the details image --%>
</asp:Panel>
<atlasToolkit:CollapsiblePanelExtender>
</ContentTemplate>
</atlas:UpdatePanel>
</asp:View>
</asp:MultiView>
</asp:Panel>
So when clicking on some control in one of the panels, TreeView, on the image or switching to another View and back to the one with the images, all Extenders (CollapsiblePanel, ToggleButton and may be others, too) stop working.
The CollapsiblePanel works, but CollapsedText and ExpandedText is no longer showed. The ToggleButtons are showed as normal Checkoboxes, which are still working. And under some circumstances clicks on one of the images are not sent to the server to be handled there (returning updated images).
I hope that will help you.
Kind regards.
Marco