Some users show up with no group membership and are getting the wrong filtering permissions as a result.
This happens when a user isn't a member of any group mapped to local Smoothwall groups. The users are instead mapped to the "Default Users" group and given permissions relevant to that group.
Make sure that all users are a member of the correct group in the directory you are mapping to the local Smoothwall groups. Changes made in the directory may take up to 10 minutes to be reflected on the Smoothwall user activity list.