The QD is on the head to make break down easier, nowhere does ISC recommend disconnecting the qd under water, a stuck solenoid requires you to fly the unit manually using the tank valve to feather O2 in. I understand if one was 2 hours back in a cave and wanted to pop the connector off, but in most cases it would be an aborted dive and RTS. If you do disconnect under water, its like Steve said, you must rinse in fresh water and dry completly before reconnecting it.