That should not be happening, as the web application is
unloaded when you build it. (Obviously) the page is being
cached somewhere. Is there a proxy between the browser and
the server? Proxies can cache pages.

Perhaps this will solve your problem:

Response.Cache.SetCacheability
(HttpCacheability.ServerAndNoCache);

on the Application_BeginRequest event in Global.asax. This
avoids caching on the browser and on any cache-capable
element between the browser and the server (such as
proxies).