If you create a forum that only users with Administrative access should be able to join.
Then the forum vanish. I had do enable view on Moderating on that forum to be able to view it (as an administrator)
I have encountered this before. It's probably the normal behavior based on how the permissions work.
The default #1 admin is a member of Registered, Administrative, and Moderating. If you set Revoke on a node for Registered then admins won't have access to that forum unless you also set an explicit Allow for one of the other two groups. This is because Revoke actually overrides an inherited Allow from another group. Only an explicit Allow can override a Revoke. I was confused by this at first so I raised the issue with the devs.
Under the current system, the better way to restrict a forum is to check the Private node box in the Node Permissions. Then explicitly allow those you want to access it (instead of restricting those you don't want to access it).
Yea but if I want a group to have access instead of just one or two users, then it's a lot of work.
The Category has Moderative access and what I did was set Deny on all groups exept the administrators, on the forum that should be hidden for everyone (except admins).