if a host has IPv4 only or IPv6 only this works fine, but when a host has both - DualStack somethimes it works sometimes only one - can be IPv4 or can be IPv6 works; and in /var/log/messages I get something like
May 10 18:51:30 dnssrvr named[2526]: client 192.168.1.2#38618: view wkst: updating zone 'ddns.local/IN': update unsuccessful: WIN7HOST.ddns.local: 'name not in use' prerequisite not satisfied (YXDOMAIN)
for several times;
Which probably means that the name for the host has already been added to dns with an IPv6 address or vice versa. Have a look at https://deepthought.isc.org/article/AA-01091/0/ISC-DHCP-support-for-Standard.... It might be relevant. I don't know. 'ddns-update-style standard' didn't even exist when I fiddled with this.