I've discovered that this is actually a bug (or badly designed "feature") in the isc-dhcp package.
I upstreamed the bug here: https://bugs.launchpad.net/ubuntu/+source/isc-dhcp/+bug/1524093
I've discovered that this is actually a bug (or badly designed "feature") in the isc-dhcp package.
I upstreamed the bug here: https:/ /bugs.launchpad .net/ubuntu/ +source/ isc-dhcp/ +bug/1524093