Verification done for isc-dhcp 4.3.5-3ubuntu1.1 as well:
If you manually enable using dhclient for ipv4 networking in the initramfs, the system behaves as expected and correctly writes DOMAINSEARCH in the /run/net-*.conf files. Ipv4 is not handled by dhclient by default (but uses klibc instead) hence the need to modify scripts.
Verification done for isc-dhcp 4.3.5-3ubuntu1.1 as well:
If you manually enable using dhclient for ipv4 networking in the initramfs, the system behaves as expected and correctly writes DOMAINSEARCH in the /run/net-*.conf files. Ipv4 is not handled by dhclient by default (but uses klibc instead) hence the need to modify scripts.