We re using one security level (and none security) for our issues. It is possible to assign an issue having a security level to a user, who is not having any permission on security levels.
So the issue dissappears: the assigned user is not seeing it and the one who has assigned it is thinking that the other one is working on it. Strange behaviour, isn t it?!
-> Is there a way to avoid that one can assign issues with sec-level to persons who will not be able to see it?