This does look like a bug … maybe. From reading the IDN spec, it seems that all domain names that have been encoded to punycode should start with xn-- , so I am confused as to why this one starts with xn---- (four dashes) ?
Ok, that makes sense now. I found a bug in the Virtualmin code where it tries to fix incorrectly converted punycode domains that start with xn— (three dashes), but this was breaking domains starting with xn---- !