I am having an issue with testing asynchronous tasks in ASP.NET & IIS7. From what I have read, the worker thread should be released back into the thread pool while the I/O thread performs the async work, allowing ASP.NET to server other incoming requests. But when I simulate heavy load on the web application by making 20 simultaneous requests to a page (async.aspx) that performs long running async tasks, I am unable to browse to some other normal aspx page until the requests are just about done. Am I misunderstanding or missing something here?

I am running Vista Biz x64, VS2008 + IIS7. I have the Async attribute applied to the Page directive.