If you’re using a custom User class (implied since you state that you’ve created a from_db method for it), it would be helpful if you posted the complete class here.
I would interpret from this comment that his problem was resolved by moving away from the __init__ implementation.
I know that I have never encountered a problem when using from_db in the Django Admin.
It is likely that there’s an issue in django-filer. I started looking at their code and I see where they are overriding __init__ in their models.