Cannot edit TXT records > 255 characters (shows wrong data, writes wrong data).
Long records are ones that will be truncated by the UDP response and requires a client to connect and retrieve the rest of the record.
In BIND, such records are defined as ("chunk1" "chunk2")
Webmin's DNS module writes them out as "thewholething" which means that BIND refuses to boot after that due to syntax errors.
This problem extends to the DKIM module too, which defaults to 2048 bit keys and stores them as one, long "quoted line", which of breaks BIND.
The fix requires something like this - haven't tested this regex (\s("[^"]+"\s)+\s*) Then take all "string1" "string2" pairs and merge them into one string. Voila, your GUI would then understand how to display multipart TXT records.
As for writing, that's the easy part. Just chunk it so that no single chunk is over 255 characters.