Donrade, you're correct, I've mistyped the password, checked btmp afterwards and it had the changed timestamp. Well, I guess, since Ubuntu is supposed to be a multiuser system it makes sense to appear this way. For a single user it may be an annoyance, but can be resolved by removing it from gconf. This said, I assume it isn't a bug then.
Donrade, you're correct, I've mistyped the password, checked btmp afterwards and it had the changed timestamp. Well, I guess, since Ubuntu is supposed to be a multiuser system it makes sense to appear this way. For a single user it may be an annoyance, but can be resolved by removing it from gconf. This said, I assume it isn't a bug then.