Always perform filtering in the backends as well
A follow-up for !38 (merged).
This matches the behaviour in the main mediator logic introduced in d16a4a10; without this change the mediator would remove users from unrelated groups.
A follow-up for !38 (merged).
This matches the behaviour in the main mediator logic introduced in d16a4a10; without this change the mediator would remove users from unrelated groups.