Same problem !
cant login , always "invalid username/password"...
i try to re register my demigod product (on the same account) and the following message appears "your serial of demigod is not an active validation" or something like that...
i try with a friend account to register the game with his serial, and its work (he dont have the login password bug)
anyone who have ths login/password bug could try to re register your demigod product ?