I have a 2004 Defender Td5 and the central locking is giving me problems.The back door does not lock when the key fob is pressed.only the 4 side doors lock.But the biggest problem is when I go to open the drivers door from inside the vehicle locks.One day our 5 month old baby was inside.vehicle running.I went to open the drivers door and as I pushed the button in with my thumb to open the drivers door the vehicle locked.Luckily the back door was not locked so I could get in and over the seats.Any ideas what's at fault?