Hi Thomas,
Hello Sumant:
Thank you for reporting this issue. A correction made in 4.3.5 under ticket 29246 that made it possible for the server to send the FQDN option to v6 clients, broke the ability to return option 17.
We will be correcting this our next feature release, 4.4.0, which is due out Q1 of 2018. We may have a patch that can be applied manually to 4.3.6 prior to that. Please accept our apologies for any inconvenience this may be causing you.
If you would be willing to test a manual patch that would be tremendous help to us.
Regards,
Thomas Markwalder
ISC Software Engineering