Versions affected: latest shipping Safari, latest nightly of WebKit (r31738) on Mac OS X 10.5.2. Steps to reproduce: 1) Register on the website (you must be a Telecom Italia customer) 2) Log in using your username and password 3) The page refreshes without logging you in This bug reminds me a lot of bug 3512, but I think <rdar://problem/4110617> should have been fixed by now. If it hasn't, please close this bug as a duplicate.
Forgot: the website works correctly with Camino and Firefox.