There are certainly some people who switch of the PA.
I used to ride up in the front carriage on a DART that had a driver change at Clontarf quite regularly and whenever there was one particular driver who got on the train, the PIS was always turned off after the change.
Could be many different units, but if that driver came on, without fail the unit would have its systems turned off. Either that or it goes off when last driver signs out and he doesnt' sign it back it.
I have seen Dublin Bus drivers do the same who do not like the stop announcements, they are not supposed to be able to do it but a few drivers know how to.