I have found this question here, but it is not clear for me. It seems that there are two values related to email confirmation in app/users.php.
define('QA_USER_FLAGS_EMAIL_CONFIRMED', 1);
define('QA_USER_FLAGS_USER_BLOCKED', 2);
define('QA_USER_FLAGS_SHOW_AVATAR', 4);
define('QA_USER_FLAGS_SHOW_GRAVATAR', 8);
define('QA_USER_FLAGS_NO_MESSAGES', 16);
define('QA_USER_FLAGS_NO_MAILINGS', 32);
define('QA_USER_FLAGS_WELCOME_NOTICE', 64);
define('QA_USER_FLAGS_MUST_CONFIRM', 128);
define('QA_USER_FLAGS_NO_WALL_POSTS', 256);
define('QA_USER_FLAGS_MUST_APPROVE', 512);
QA_USERS_MUST_CONFIRM and QA_USER_FLAGS_EMAIL_CONFIRMED. One is the opposite of the other?