I just got off the phone with a client who is using the MS-AJAX TabControl in one of his applications and any time he causes a postback, the tab resets to the first tab.
If you’ve never seen the problem, you’re lucky. There are a couple of ways around the problem. The first and easiest if it works in your situation is to put the tab in an update panel so that you never actually do a full postback.
However, there are times when this won’t work. In this particular case it is because one of the tabs holds the file upload control, which can’t be used inside an update panel. (Another problem we had to find a way around last week.)