Some customers discovered that sometimes switch to Design view was very slow. We analyzed submitted reports and tracked the issue down to a code that was discovering available AJAX Extenders and which contols they were applicable to. In order to avoid unnecessary delays we moved discovery of AJAX extenders to a background thread. This made switch to Design view significantly faster since designer is now available immediately while extenders are still being enumerated. Here is a screenshot, look at the status bar that shows "Discovering AJAX extender controls..." and displays a small progress indicator: If you select a control before applicable extenders are discovered, the control will not display its smart task menu and/or will not...(read more) ...
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