I realise that.
OK if I go into Group management there are 22 members listed in the group "Moderators" which is group 3 and one of the unremoveable ones.
The guy I changed to global and then back to moderators is listed there.
If I go into any of their individual profiles and their permissions they are in the group Users (checkbox) and Moderator (radio button).
If I go into the permissions for the Moderators group they have a 1 next to everything to do with the forum (read, post, see etc) and I have re saved that.