In Zammad, when using @@ to search for a user, the expected user does not always appear as the first result. Instead, a member of a group associated with that user may be displayed first, which can lead to confusion when selecting the correct user.
We experience the same behaviour. I think this has something to do, with the person you set as replacement when you are out of office.
I am also interested if this is a bug and how change this behaviour.