That's right. But the solenoid lock actuator or the pin it slides can get stiff, so that it stays locked even when signalled to unlock. Also a loose or sticky mechanism can lock if the gate is slammed too hard.
Or the whole central locking mechanism can be too sensitive. The return spring in the switch operated by the driver's door button can get week, so the button develops a tendency to switch on (ie lock) under gravity. A jolt to the car, such as slamming the tailgate, can trigger this. The cure is to renew, or wind a turn of sticky tape round the button so that it is slightly binding in its guide.