So I've been using my 5s for about 15 hours now and I've noticed every so often the screen will dim slightly by itself. If I go to the brightness setting if it is around 70% up the bar no matter how much further to 100% I go it remains the same brightness unless of course I go below 70% and then the screen gets darker. There is no way to make it brighter. After about 5 minutes maybe more the screen goes back to the brightness it was on. Very strange, anyone else had this yet?