You want users to behave, and them knowing an admin is present will make them behave, yes that is a given. But at the same rate, if the users are going to misbehave when an admin isn't present, it's better they don't know they're there.
I don't know if I agree with punishment, this feels a bit too much like shooting yourself in the own foot to enforce. Someone calls an admin in for help, then says it like a goof and ends up getting banned, might make people less likely to want to call an admin in. But, I do think if this does happen, the admin should simply tell the person not to do it.
There are arguments for and against, but I just think there is enough trouble for admins to enforce the current rules they have (friendlying in particular) that adding more will make things too complex. A simple talking to would more than likely correct this problem.