Assign hostname by MAC address with dynamic IP

[jp0469]

In prior versions of OPNsense, I could use the static mapping feature to associate an assigned hostname with a client's MAC address, while leaving the IP address field blank. The result would be that the client receives a dynamic IP but the assigned hostname shows up in the "Leases" page and that hostname could also be used to reach that particular client. Since updating to 21.7, that functionality no longer works. The hostname doesn't resolve and also does not show in the list of leases. Any idea what might have changed?