Since last Friday - article here. Of course, it makes no sense at all to have them in the priority lane and not in the regular lane, or vice versa. If you wanted to sneak through with your underwear loaded with C-4, you could buy a ticket in First or Coach depending on where the magnetometers were and go through the appropriate lane without backscanners. To err is human, to really screw up on a massive scale requires government action.