Issue Plesk continues to write deleted slave DNS server in /var/named/chroot/etc/named.conf

[mr-wolf]

I have a Plesk server which I use as authoritative server for all my clients. On my other Plesk servers I have not installed the DNS-option of Plesk.
The advantage of this is that I have all DNS in one place which also allows me to do some creative things.

On that server, ns6.<mydomain>, I have installed the "slave DNS manager" in which I configured ns5.<mydomain> as a slave server.
On ns5.<mydomain> I have installed bind and configured it as a slave DNS-server for ns6.<mydomain>.
This bind is therefore independent of Plesk.

This is all working fine.
2 years ago I decided to add a 2nd slave DNS-server on ns4.<mydomain> and configured this in my extension.
But because I didn't want to change all the nameservers in the Internet-registry I abandoned the idea.
I deleted the IP (81.14.147.34) of the ns4.<mydomain> in Plesk's "slave DNS manager" and thought it was ok.

Only recently did I find out that Plesk is still writing the IP (81.14.147.34) of ns4.<mydomain> in the section "allow-transfer" of /var/named/chroot/etc/named.conf

I can use sed to correct this by issuing

sed -i '/81.14.147.34;/d'  /var/named/chroot/etc/named.conf
killall -HUP named

Each modification of DNS will add the IP of ns4.<mydomain> in allow-transfer.
Where does it get that data????

So entries in /var/named/chroot/etc/named.conf should look like this:

zone "client.com" {
        type master;
        file "client.com";
        allow-transfer {
                84.203.11.86;
                common-allow-transfer;
        };
};

But recently modified domains look like this and named will try to push the zone to a DNS-server which I haven't configured for this anymore.

zone "client.com" {
        type master;
        file "client.com";
        allow-transfer {
                81.14.147.34;
                84.203.11.86;
                common-allow-transfer;
        };
};

In the folder /usr/local/psa/var/modules/slave-dns-manager there is only 1 file and that's slave_84.203.11.86.conf

Which code is still pushing 81.14.147.34 into the allow-transfer sections?
Where can I alter a file or database entry to stop this??