Note that this is just a UI issue. The model allows this; you can do something like this via the API:
maas admin interface link-subnet hn4sr6 46 mode=static subnet=2001:db8::/64
Note that this is just a UI issue. The model allows this; you can do something like this via the API:
maas admin interface link-subnet hn4sr6 46 mode=static subnet= 2001:db8: :/64