If you use a bad username/password combo to force the user to log out, the following happens:

First, the user wants to visit the secure site...
Browser: GET /secureplace/file.html
Server: 401 Unauthorized Authenticate Realm
Browser shows user a password prompt for the realm "Realm"
Browser: GET /secureplace/file.html AUTHENTICATION Realm username:pass
Server: 200 OK

Then the user clicks a link. Since the browser remembers that this directory requires authentication, it automatically includes the username and password.
Browser: GET /secureplace/otherfile.html AUTHENTICATION Realm username:pass
Server: 200 OK

If you use any process to change the login, such as using a URL with a bad username and password embedded, the following will occur:
Browser: GET /secureplace/someotherfile.html AUTHENTICATION Realm baduser:badpass
Server: 401 Unauthorized Authenticate Realm
Browser: GET /secureplace/someotherfile.html AUTHENTICATION Realm knowngooduser:knowngoodpassfromcache
Server: 200 OK

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