My wife has had this 2015 M2 for a while now, and only just noticed that when leaving the car and locking it, we find the boot doesn't lock straight away.
It's fine after a while though.
This can't be normal, can it?

 

By chance do you have your key in your pocket.

on mine, if I have the key in my pocket I can open the boot of a locked car. Works on proximity I guess.