Sometimes button to add user to org is missing

How to reproduce

• Login with user that has admin rights (e.g. user frentix on test9)
• Search for a user, e.g. "gnaegi"
• => NOK: button to add user to other org is missing

There is a button normally, don't know why not for this scenario. Maybe because the user has "only" admin rights and not explicit user manager rights?

The issue is that the user "frentix" is only admin. in one organisation but system admin. of the system. As system admin can the user see all organisations which is not wanted.