ifupdown_0.8.17ubuntu1.1 doesn't assign static ipv4 and ipv6

Upgraded from 16.06 to 18.04.5. 1 interface has issues coming up. The only thing that is different is that this interface has both ipv4 and ipv6 addresses.

eg
auto eth6
iface eth6 inet6 static
        address 2001:1ffb:ffe:1::3/64
        gateway 2001:1ffb:ffe:1::1
        dns-nameservers 2001:1b3b:ffff:ffff::71 2001:1b3b:ffff:ffff::72 2001:4860:4860::8888 8.8.8.8
iface eth6 inet static
        address 10.155.240.122/29
        gateway 10.155.240.121
# dns-nameservers 8.8.8.8

If I comment out either the v6 or v4 config, then it works.
Also v6 seems to show dadfailed tentative until I down and up the link, then the ip address is gone

jsvm-1a-de:~$ ip -c address list dev eth6
8: eth6: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 52:54:00:9e:f3:76 brd ff:ff:ff:ff:ff:ff
    inet6 2001:1ffb:ffe:1::3/64 scope global dadfailed tentative
       valid_lft forever preferred_lft forever
    inet6 fe80::5054:ff:fe9e:f376/64 scope link
       valid_lft forever preferred_lft forever
jsvm-1a-de:~$ ip link set dev eth6 down
RTNETLINK answers: Operation not permitted
jsvm-1a-de:~$ sudo ip link set dev eth6 down
jsvm-1a-de:~$ sudo ip link set dev eth6 up
jsvm-1a-de:~$ ip -c address list dev eth6
8: eth6: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 52:54:00:9e:f3:76 brd ff:ff:ff:ff:ff:ff
    inet6 fe80::5054:ff:fe9e:f376/64 scope link

I believe this is due to https://bugs.launchpad.net/ubuntu/+source/ifupdown/+bug/1510098
as if I add pre-up echo 0 > /proc/sys/net/ipv6/conf/eth6/accept_dad
the link come up with both addresses.
       valid_lft forever preferred_lft forever
jsvm-1a-de:~$

jsvm-1a-de:~$ sudo apt list --installed | grep net-tools

WARNING: apt does not have a stable CLI interface. Use with caution in scripts.

net-tools/bionic,now 1.60+git20161116.90da8a0-1ubuntu1 amd64 [installed]
jsvm-1a-de:~$ sudo apt list --installed | grep ifupdown

WARNING: apt does not have a stable CLI interface. Use with caution in scripts.

ifupdown/bionic-updates,now 0.8.17ubuntu1.1 amd64 [installed]
jsvm-1a-de:~$