Hello Darren:

The ISC DHCP project has been migrated to gitlab:

https://gitlab.isc.org/isc-projects/dhcp

where you may obtain the source, participate in development, and see or submit new issues.  For historical purposes the ISC DHCP RT bugs will remain available for quite some time to come.

We recently had this issue reported there by another user:

https://gitlab.isc.org/isc-projects/dhcp/issues/6

And hence updates on the matter will be available there. 

Regards,

Thomas Markwalder
ISC Software Engineering