The OA name server hostnames are resolved to public and private IP addresses simultaneously:
# dig +short ns1.example.com 192.0.2.2 203.0.113.2
There are no corresponding A-records for the private IPs in the zone
example.com. There are only A-records for the public IP addresses. The name server is running PowerDNS.
The name servers were registered in OA with the names like
ns1.example.com. Later, the zone
example.com was added to OA, so it is hosted on the servers
ns*.example.com. In such situation, the zone should have so-called glue records (A-records resolving NS hostnames to their IPs) for proper DNS server functioning. These glue records are usually added manually on the zone creation, however PowerDNS module adds such records automatically, taking IP addresses the NS were registered with (in this example, the backnet IPs).
As a result, the zone
example.com running on the PowerDNS contains 2 A-records per NS: one is a manually added one, another is an auto-created with the backnet IP. Such behaviour was acknowleged as a software issue #POA-114360.
Please contact your TechnicalAccount Manager in order to clarify the current status of the software issue.
To workaround the issue, please contact Odin Technical Support.