It's not really a change, but a small fix. The issue it fixes is that some phones wake up on the charger and don't go back to sleep, like they should. So you'll find the phone on in the morning. I actually have that bug from 4.3 and am not in any hurry to install the MK2 fix. Only happens every 2+ weeks or so, so it's just not worth the hassle of going back to stock to put it on.