RNDC for Dynamic Zone
A dynamic zone cannot be updated manually, to be able to do that, you must call "rndc freeze yourzone.com" then you can update the zone file, and after you must re-enable the zone by typing "rndc thaw yourzone.com".
... Guess what? Webmin can enable you RNDC, but does not send those commands when the zone is dynamic. G.
-f.