hiong

there are several sensors in the car, if the key fob is detected by the sensors in the car cabin only (I think there are 2, covering front seats and rear seats respectively), putting your hand on the handle should not unlock the car. this is actually very logical because if you are the one driving and is inside the car with the key, you wouldn't want a stranger to be able to unlock your door just by putting his or her hand on the handle.

hiong

this scenario is different from kpatrick4's scenario. in your scenario, the interior trunk sensor (there are 2 for the trunk, one to detect interior, one to detect exterior) is picking up the key fob, hence allows you to unlock the trunk without the exterior sensor picking up the key fob. I guess this is sort of a convenience feature, to prevent accidental locking of your key fob within the trunk.

kpatrick4's key fob was in the cabin, not in the trunk, hence it was picked up by a different sensor. if I recall, there are a total of 8 sensors, one in each door to sense external, 2 internal cabin sensors (1 for front, 1 for rear), 2 trunk sensors (1 internal, 1 external). the behaviour of the central locking system should be dependant on which sensor is picking up the key fob.