Yes, that is a deliberate function on all Thatcham approved central locking/alarm systems to prevent accidental unlocking. As said, a door must be opened or it will re-lock. This is also why you MUST NOT put your keys in the car when you remote unlock the car unless you are getting straight in. Just the other day I got called out to a driver who had put the keys on the floor whilst strapping their toddler in, but the door-open switch was not working, the system re-armed and the doors re-locked. The driver shut the door and realised the keys were inside, but then could not open the door. Anyone want to guess how I got the car open? you wont tell us anyway :D