It seems that this was a coincidence... sometimes AD users are found but
most of the time they are not:
[root@ipaclient sssd]# id usera(a)bau.mydomain.at
id: usera(a)bau.mydomain.at: No such user
[root@ipaclient sssd]# id userb(a)bau.mydomain.at
id: userb(a)bau.mydomain.at: No such user
Where do I have to take a closer look?
Cheers,
Ronald