ISC-DHCP-Server removes wrong dynamic DNS-Name from the DNS-Server

I'm using Debian Bullseye to run KVM (Kernel-based Virtual Machine) with two guests vdeb02-10-base and vdeb03-10-base. Both guests have Debian Buster installed. For testing purposes vdeb03-10-base is just a clone of vdeb02-10-base, using the virt-clone utility to ensure that is has unique system parameter like mac address etc. On all devices (host, guests) I use **systemd-networkd**. If I start vdeb02-10-base with DHCP enabled to get an ip address from my ISC-DHCP-Server everything works fine as shown by the log of the DHCP-Server: Oct 05 18:43:49 vnetsvr30-10 dhcpd: DHCPDISCOVER from 52:54:00:ee:f5:0a via ens1 Oct 05 18:43:50 vnetsvr30-10 dhcpd: DHCPOFFER on 192.168.30.104 to 52:54:00:ee:f5:0a (vdeb02-10-base) via ens1 Oct 05 18:43:50 vnetsvr30-10 dhcpd: DHCPREQUEST for 192.168.30.104 (192.168.30.10) from 52:54:00:ee:f5:0a (vdeb02-10-base) via ens1 Oct 05 18:43:50 vnetsvr30-10 dhcpd: Wrote 56 leases to leases file. Oct 05 18:43:50 vnetsvr30-10 dhcpd: DHCPACK on 192.168.30.104 to 52:54:00:ee:f5:0a (vdeb02-10-base) via ens1 Oct 05 18:43:50 vnetsvr30-10 dhcpd: Added new forward map from vdeb02-10-base.home.hoeft-online.de. to 192.168.30.104 Oct 05 18:43:50 vnetsvr30-10 dhcpd: Added reverse map from 104.30.168.192.in-addr.arpa. to vdeb02-10-base.home.hoeft-online.de. The dynamic DNS name is mapped to the DNS server so I can query for it with ~$ dig +search +noall +answer vdeb02-10-base vdeb02-10-base.home.hoeft-online.de. 3600 IN A 192.168.30.104 If I start then vdeb03-10-base the DHCP-Server log shows me this: Oct 05 18:44:55 vnetsvr30-10 dhcpd: DHCPDISCOVER from 52:54:00:ed:c5:df (vdeb02-10-base) via ens1 Oct 05 18:44:55 vnetsvr30-10 dhcpd: ICMP Echo reply while lease 192.168.30.104 valid. Oct 05 18:44:55 vnetsvr30-10 dhcpd: Abandoning IP address 192.168.30.104: pinged before offer Oct 05 18:44:55 vnetsvr30-10 dhcpd: Removed forward map from vdeb02-10-base.home.hoeft-online.de. to 192.168.30.104 Oct 05 18:44:55 vnetsvr30-10 dhcpd: Removed reverse map on 104.30.168.192.in-addr.arpa. Oct 05 18:44:57 vnetsvr30-10 dhcpd: DHCPDISCOVER from 52:54:00:ed:c5:df via ens1 Oct 05 18:44:58 vnetsvr30-10 dhcpd: DHCPOFFER on 192.168.30.95 to 52:54:00:ed:c5:df (vdeb03-10-base) via ens1 Oct 05 18:44:58 vnetsvr30-10 dhcpd: DHCPREQUEST for 192.168.30.95 (192.168.30.10) from 52:54:00:ed:c5:df (vdeb03-10-base) via ens1 Oct 05 18:44:58 vnetsvr30-10 dhcpd: DHCPACK on 192.168.30.95 to 52:54:00:ed:c5:df (vdeb03-10-base) via ens1 Oct 05 18:44:58 vnetsvr30-10 dhcpd: Added new forward map from vdeb03-10-base.home.hoeft-online.de. to 192.168.30.95 Oct 05 18:44:58 vnetsvr30-10 dhcpd: Added reverse map from 95.30.168.192.in-addr.arpa. to vdeb03-10-base.home.hoeft-online.de. Why does the DHCP-Server mean that the DHCPDISCOVER comes from vdeb02-10-base and not from vdeb03-10-base? Mac address and hostname are different. Of course the DHCP-Server then means there is an ip address conflict on the network using the ping test. Then it removes the DNS mapping for vdeb02-10-base and replaces it with the mapping for vdeb03-10-base with the result that I cannot resolve the name for vdeb02-10-base anymore. What's going on here? Why does the DHCP-Server replaces the hostname on the DNS-Server instead of just adding the name of the second guest? Where could be the problem? At the guests, or at the host with a standard network bridge for the guests, or at the DHCP-Server, or by using systemd-networkd? Maybe there is an option to be used in /etc/dhcp/dhcpd.conf?