Hi Heather,
I've got a 2012 model and can confirm that once I unlock via central locking it automatically locks again if I don't open any doors within a set time.
If I unlock any door (front, rear, barn) it doesn't relock, I actually went and checked each individual door.
I think you have a safety issue. I recently read of this happening to a mother who put her child in the childseat and left her bag in the car at the same time, it automatically locked and she had to call 000.
I'll try and find the link to this later tonight for you.