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 have “Add Extender…” menu item. 

Unfortunately, if control is selected, due to architectural limitations we cannot update its smart task availability. Therefore you may have to unselect and reselect the control in order to let it update its smart task menu.