Mine's been fine all day since the update, until I got home. Now I'm sitting in my chair - where the light is arguably not quite dim but not quite bright - and it's acting like it doesn't know what brightness setting it should be on. It doesn't go from dimmest to brightest, but it is kinda like... "ok, let's dim a little bit! no, wait, brighten up a tad! no, too bright, dim down some! Er, no, go bright!"
It's not happening very rapidly, maybe about every 10 seconds or so it changes a bit. Definitely new behavior, it didn't do this prior to the update. So they definitely changed something... which is odd, because I don't recall any reported problems related to auto-brightness which would require changes.