The custom fields are saved and shown in the Web UI/Django object
The custom fields are empty. (The Django objects .cf is also an empty dict)
Custom fields for other objects (e.g. Prefixes) work as intended.
Getting the same result here as well. From initial testing pre-existing addresses and unmodified fields are working as expected.
Looks like secrets are also affected.
The problem is a missing call to super().clean() on the model forms; an easy fix. Thanks for the report!