[carrera.owner]

Questions: (i) Was your iPhone in direct sunlight for any length of time when you first observed this? And, (ii), is the problem gone? If you answered yes to both of these questions then maybe you temporarily changed the properties of the screen (brought about b/c of sunlight-induced heating of the screen). I suggest this b/c some displays (on other electronic gadgets) will suffer if left in direct sunlight.