Hi Peter,
Same problem here.
I found this post regarding your question : http://forum.mikrotik.com/t/dhcpv6-duid-change-bug/108009/1
I was running vmware so I could change the interface mac-address and check that the DUID also changed.
It didn’t solve the problem : I still don’t get an IPv6 address.
Did you make some progress on this issue ?
Thanks,
Arnaud