After the recent upgrade to android 6.0 on my LG G3, I've noticed something strange.
I use the optional home button at the bottom of the home screen for the 'capture+' function to create a screenshot that you can mark up with notes.
After the marshmellow update this button now turns the light on. When I disable the up button function in the Key Plus app, then home button doesn't do anything but turn the screen off.
I'm guessing that something about the way LG has mapped the up volume button to the 'Capture +' note function has possibly interfered here?
EDIT: I now notice that this optional home screen button now initiates whatever app you have selected to activate in the KeyPlus app. In lolipop this was not the case. The home screen button for capture+ worked correctly, but now this button activates whatever you have set in KeyPlus to bind to the up volume button.