Everything was fine with 7.4.2, then upon upgrading to 7.5 it soon became apparent that some users had read and write access to a private forum in which they were not supposed to. They were all members of the Moderators group, they were not global moderators, and they were not a member of any group that had access to the private forum, but they were able to get to it via the active topics screen. Once in the forum they were able to read threads and post.