When jabber messages are disabled in ACP, but email - enabled, the user can only switch between no notifies and email notifies, and he is aware that there are no working jabber notifies.

When emails are disabled in ACP, there is nothing in UCP that indicates it. Users can still select between jabber, email, and no notifies, but email notifies won't work. So a user can select not working option, but if he knew that it is not working, he might better select jabber notifications.