I had a deficient battery for the last two weeks that kept rapidly draining and shutting the phone off. AT&T sent me a replacement on Saturday, and it's worked fine since then.
Yesterday, I upgraded my OS from 4.2 to 18.104.22.168 and ever since then, I've had issues with a sporadic keyboard and trackball light. Sometimes it won't even come on for hours at a time, other times when it does come on it doesn't last long. As of right now, it hasn't worked all day.
When I have the phone out in the light, the trackball and keyboard do not come on. I then took the phone and put it under my desk in the dark and they both came on. I let the screen shut off and brought it back in the light and turned it on again and they didn't light up, but they did again when put back in the dark.
However, this morning when I went to first use my phone, it was dark in my room at home and they did not come on.
I've started to get used to it now, I also love how the screen becomes VERY bright out in the sun now. That's a huge improvement, and I'm really starting to like the light sensor for the trackball as well.