When creating a Reverse Master Zone using Webmin 1.580, only a full IP address is accepted in the "Domain Name / Network" field. For example, entering "192.168.1." causes the following error: "Failed to create master zone : '192.168.1.' is not a valid network"
Entering 192.168.1.0 will allow Webmin to proceed, but causes reverse lookup to fail because of improper filename and PTR records (0.1.168.192.in-addr.arpa.) My work around was to manually fix the filename and PTR records by removing the "0".
Environment: Ubuntu Server 10.04 LTS