Ok this is what I just noticed today. I recalibrated my optical sensors again in a dark room (I am on Portico) and the capacitive touch buttons stay illuminated when in dark environments. The moment I turn WiFi on, the lights go off and screen brightness increases in a dark to low light room. Now when I turn off Wifi again the screen brightness decreases and the capacitive buttons lit up. It is really weird for the buttons to not stay lit in a dark room.
I think this is a bug with the Portico update or am I the only one experiencing this?
It's a Portico bug - lots of people are having issues with brightness and that includes the buttons. You could turn it on outside in the brightest of days and the screen would be set to max brightness and the buttons will all be lit up. 10-20 seconds later it MAY adjust itself and lower the screen brightness and turn off the button lights... but then again, it may not. Sometimes, if you relock and unlock your phone again, the brightness will be corrected.
Only real solution is to turn off auto brightness control if it really bothers you. Some people say if you turn on the phone in a completely dark room it will be fixed but that doesn't seem to fix the problem for me for longer than a few minutes.