Starting from 4.4 we have official and documented way how to use DNS as default interface
(Usig HostInterface or HostInterfaceItem agent configuration parameter)
When server\proxy recieves autoregistration request without HostInterface[Item] it fills listen_ip with IP adress and listen_dns with DNS adress that was resolved from IP
If such resolving is configured incorrectly (in my case IP resolved in _something) - it breaks auto-registration with process_autoregistration_contents(): "_something" is not a valid hostname
Potentially dns name can be used in auto-linked templates in a macro {HOST.DNS}
But we should at list add this note to the documentation as because functionality that might not even be used breaks down the functionality that is configured correctly according to the documentation