This walkaround doesn't work for me.
I switched to the console before applying settings on confirmation screen, and issued commands (replacing "my_domain.com" with valid domain name):
chroot /target /bin/bash
ucr set --force domainanme="fanina_sa.local"
ucr set --force kerberos/realm="FANINA_SA.LOCAL"
I had to define different domain name on domain definition screen (as fanina_sa.local pattern was not valid) and after confirmation UCS systems 4.0 fell into infinite loop during initial configuration with message on console #4 - that some file in /etc is missing (now I don't remember what was the name) - I tested it 4 times.
UCS 4.1 was able to complete initial configuration, but after first reboot web-based console is inaccessible (but there is an access to commandline).
There is probably most accurate log from management-console-web-server.log:
File "/usr/lib/python2.7/dist-packages/saml2/config.py", line 372, in load_file
mod = self._load(config_file)
File "/usr/lib/python2.7/dist-packages/saml2/config.py", line 366, in _load
File "/usr/lib/python2.7/importlib/__init__.py", line 37, in import_module
File "/usr/share/univention-management-console/saml/sp.py", line 55, in <module>
with open(CONFIG['cert_file'], 'rb') as fd:
IOError: [Errno 2] No such file or directory: '/etc/univention/ssl/unassigned-hostname.fanina_sa.local/cert.pem'
I also tested 'normal' installation on this machine to eliminate specific hardware influence - creating valid domain name leads to successful domain foundation.
It looks like there should be something more to define/set. I'm looking forward for any additional tip. Maybe it is possible to force new domain name after initial configuration ...