OK.
I created 2 reverse zones:
1.168.192.in-addr.arpa
100.168.192.in-addr.arpa
Then I continued and created a host via WebUI.
The host is displayed with correct hostname, however there's an error displayed:
The host was added but the DNS update failed with: All nameservers failed to answer the
query for DNS reverse zone 47.1.168.192.in-addr.arpa.
What is causing this error?