Gotta love the security. One time I wasted about four hours looking for a switch. Turned out to be part of total unrelated setting. Have you verified that the button is grayed out before the user enters and order? In the back of my mind, I recall that if you didn't change the defaults BEFORE entering the first order, it was unavailable for the rest of the session. Sorry I don't have an exact answer. It is very frustrating.