Hi, and thank you for the report — you are right, and we found exactly where it goes wrong.
The help text under the field is correct: leaving it empty is a supported choice. What was overriding it is a start-up routine whose job is to fill the shared nameservers in on a brand-new install, derived from the server hostname. It decided "this is a new install" by checking whether the server has any DNS zones yet. On a server that deliberately has no zones — because its domains use external DNS, which is exactly your case — that assumption is wrong. You clear the field and save, the empty value really is stored, and then the next backend start (an update counts) fills it in again. The ns1/ns2 values you are seeing were derived from your server's hostname.
On a server that has at least one DNS zone, clearing the field already persists; we confirmed that on our own installation. So the problem only appears on installations with no zones at all.
We have prepared an update for this. The routine now leaves those fields alone once the initial setup has been completed: before setup nobody has made a choice and the default is helpful, after setup every value in that form is the operator's — including an empty one. It is in panelica-server 1.0.575, currently on the beta channel, and it will move to the stable channel shortly. After updating, clear the field once more and it will stay empty.
On your second question — removing DNS management for specific domains: there is no per-domain switch for that today. A local zone is always created when a domain is added. However, that local zone is only consulted by this server's own BIND. As long as the domain is not delegated to this server at your registrar, the world uses the external nameservers you have set and the local zone is simply unused, so external DNS works regardless. If you prefer the zone gone, you can delete it in DNS management — just note that with the current build, deleting every zone is what re-arms the behaviour above; with 1.0.575 that is no longer the case.
We have noted the per-domain "do not manage DNS" option as a feature request. Thanks again — this one was worth reporting.
