DNS server not available when trying to create a secondary dns zone

short description

I have 2 DNS servers set. Logged as admin, when i try to add a secondary dns zone with my second DNS server it is added but with an empty server field

correct behaviour

The new entry must have the server2 dns server set.

environment

Server OS: Centos
Server OS version: 7 ISPConfig version: 3.1.13p1

screenshots