The phenomena you see is because of your browser configuration.
Pls go to tools|Internet Options|Security, Click on that "Custom Level".
You will see you have enabled Cookies. Whatever you are talking about,
I can assure you that the browser "remembers" the password because
the server-side programm have put the password into the cookie. Without cookie, the browser cannot remember anything. To solve your problem, you make set the age of your cookies, or try to expire the cookie as the user close the browser.

Hope some other guys can give you more expert answers.