Ok, this is under bind dns under server templates.
I configure several other nameservers in this box. Reading the popup help, it says "f you are manually configuring other nameservers to be secondaries for domains created using Virtualmin, you should add their hostnames to this text box." While it does do that, it does not add them to the allow transfer from options for the domain in bind, meaning, the slave cannot do the download of the domain, making it useless. Unless one then goes back and changes this in webmin of course to allow the transfers.
Personally, I see no issue with allow all for transfers. But, that's up to you guys. Still, I think that the slaves should be allowed to do the transfer at a minimum...
Even better would be to respect the setting in webmin for zone defaults. I have that changed to allow transfer from listed, and listed shows any. If it would respect that, it would be wonderful and solve all issues.