All NS records are considered by application as System Records and cannot be edited or deleted.
It is not valid behavior.
Of course NS records can be used not only as self-pointing zone assignment (like SOA) but also for delegation of subdomains.
GUI allows to create NS records only via "Bulk" option and after that it cannot be modified as it is marked as "System Record".
While adding record via single entry form, NS record type is not an option at all.
All NS records are considered by application as System Records and cannot be edited or deleted.
It is not valid behavior.
Of course NS records can be used not only as self-pointing zone assignment (like SOA) but also for delegation of subdomains.
GUI allows to create NS records only via "Bulk" option and after that it cannot be modified as it is marked as "System Record".
While adding record via single entry form, NS record type is not an option at all.