Lol this was from ages ago.
Anyway, what I've found is that if I'm driving, doors locked, then I park and open the door locks (double pressing the door open button on the car door), the boot won't open until the driver's door has been opened (can be closed straight away). Haven't tested it for other doors (have 5dr).
Guess maybe it's some kind of security feature?
Does it happen to anyone else?