I think this needs to be said simpler.
YOU MUST TURN THE GOD DAMB BOTTLE VALVE OFF, BEFORE REMOVING THE BOTTLE.
AND BEFORE YOU REMOVE THE BOTTLE, AND AFTER YOU HAVE TURNED THE BOTTLE OFF. YOU MUST SHOOT THE MARKER UNTIL IT WILL SHOOT NO MORE,
AS THERE IS A SMALL AMOUNT OF GAS LEFT IN THE SYSTEM BETWEEN THE BOTTLE MOUNT AND THE MARKER, WHICH WILL MAKE IT DIFFICULT TO REMOVE THE BOTTLE, AND DESTROY YOUR BOTTLE O-RING.
Sorry to have to make this more obvious, but i fell this is getting confusing, no offence intended, we all learnt these things, some the hard way.
Good luck, Tom.