If you set someone as a forum moderator by going through Users > Moderators > Create New Moderator
Give them 'Forum Moderator' Permissions for a specific forum and tick the box for 'Edit post by anyone', for example.
You can then go to the Note Tree and check the permission of the forum you have set them as a moderator of and see that user has specific permission set for that forum, as you would expect.
From there, if you remove the permission for them to be able to edit posts it doesn't un-tick the box in the moderator setup that you originally did. So it looks like they still have the permission to edit posts in there but they haven't because it's been removed through the node permissions.
Hope that makes sense.