IE Postbacks Fail After a Few Seconds When Connecting to ASP.Net 4.0 in Localhost

I noticed an odd problem when developing a web site project on localhost using ASP.Net 4.0, IIS 7.0, and IE8. Postbacks do not work after the page has been idle for a few seconds, like 30 seconds or less. If I load the page, enter some data, and click the submit button immediately, the postback works perfectly, but if I let the page sit for not more than 30 seconds, the progress bar and the little preloader circle on the tab churn endlessly and the response never occurs.

I am unable (or don't know how) to use Wireshark in Windows to see what is actually happening on the network.

There is an exact copy of the web site on a remote server, and when connecting to that site, the problem does not occur.

Furthermore, when connecting to the site on localhost using Firefox, the problem does not occur.

Finally, when connecting to an ASP 2.0 web site on localhost using IE 8, there is no problem. The page can sit for an hour and a postback will still work.

Anyone have any ideas?