I just updated my BlackBerry Q10 to 10.3.1.1581 and I noticed something odd that wasn't happening to me when I was using 10.2. If I have the setting configured to "Allow Power/Lock Key to Unlock Device: ON" I'll check just my lock screen without unlocking the phone by pressing the w, e, r, s, d, f, z, x, or c keys ( as I always have). If I don't have any notifications, in 10.2 I'd hit the "power/lock" button and the phone would sleep again. BUT if I do the same in 10.3.1 it unlocks my phone fully. If I press "K" to wake the screen and I have no notifications and I want the screen to turn off again I have to wait 15+ seconds for it to timeout... as oppose to just pressing the power/lock button...
Does this happen to everyone? It's just a minor annoyance, but still.
Not sure where you got the "K" from but it has to be a number to show the lock screen. I can press the power/lock button on the top and it goes back to sleep mode.