If a use a ToggleButtonExtender on CheckBoxes within a Panel (or UpdatePanel) on which a CollapsiblePanelExtender operates, then the extended toggle images stay visible if the the Panel is collapsed.

Am I missing something?

I got around this issue by setting the Acordian pane to relative rather than absolute.

1.) Add reference to CSS class

 ContentCssClass="toggleRelative"
<cc1:AccordionPane ContentCssClass="toggleRelative" HeaderCssClass="" ID="AccordionPane1" runat="server" Height="100%" Width="100%">

2.) Add the following your CSS

.toggleRelative

{

position:relative;
}

Thas should keep the images set rather than floating.