in the mysql-schema-4-sp.sql the procedure TigUserLogout is defined as:

create procedure TigUserLogout(_user_id varchar(2049) CHARSET utf8)
begin
update tig_users
set online_status = greatest(online_status - 1, 0),
last_logout = CURRENT_TIMESTAMP
where user_id = _user_id;
end

why in the where clause is used directly the "_user_id" (that is not indexed on mysql) instead of "sha1_user_id = sha1(lower(_user_id))" as done in the other stored procedures?