Obscure ASP.NET Problem - AJAX Control Toolkit, CollapsiblePanelExtender, Image controls pages loading more than once....

Had an issue on a current project where a page was being loaded twice for each request, although it was a little different for each browser. Under IE, this particular page was loaded, then the 'Default.aspx' page in the same directory was loaded. In Firefox, the same page was loaded twice. This was verified by simply placing breakpoints in the Page_Load events and watching it get hit twice, in addition to seeing this via the NET monitor in Firebug (the Firefox addin).

It was causing performance issues as well as weirdness regarding page state, as you can imagine. So in I went, thinking it should be relatively easy to debug. Turns out it was quite obscure and took more time than I had originally anticipated.

http://weblogs.asp.net/pglavich/archive/2007/09/09/obscure-asp-net-problem-ajax-control-toolkit-collapsiblepanelextender-image-controls-pages-loading-more-than-once.aspx