DHCP static mapped hostname to DNS resolver, without specifying IP

[u89]

Hi. I configured DHCP Static Mappings for an interface without providing IP address (only MAC + hostname). So I want the IPs to be assigned from the poool and DNS resolver to get the mappings and serve them but unfortunately it doesn't work. I've got  Register DHCP static mappings option checked under Unbound DNS -> General.
DNS resolution works fine when I add an IP address to DHCP Static Mappings but this is not the way I want to go.

As you can see on a screenshot, devices get leases but no hostname assignments.

The situation was described on Netgate forums:
https://forum.netgate.com/topic/125306/dhcp-static-mapped-hostname-to-dns-resolver-without-specifying-ip

People claim this might be pfSense bug, so maybe it was inherited by OPNSense.

Any clue how to get things work? Or maybe someone can confirm that this is a bug in fact.

[u89]

This is how it ended up:
https://github.com/opnsense/core/issues/2946#issuecomment-493452319