It took me a little while to figure out what was happening when these abberations happend, but the crux of it is even though your sensor doesn't have the star on it, doesn't mean the light from that star isn't landing just off the edge of sensor. When this happens itll be hitting something just off the side of your sensor and send light skimming across... shabam there you have it , so move the horse down lower to the bottom of the image then you will find that the flare will decrease other wise you might have to try turning it around about.
Good luck
