I would imagine as common as flash lighting can be, it affects a small percentage of sets. Otherwise, there would be thousands and thousands of posts for all TV manufacturers as it happens across the board. That being said, it does happen. My KDL-52EX701 has light leaks akin to flash lighting. It's not visible straight on but from angles and appears as blue-ish light leaks from the bezel.. I have ignored it since it's only seen from standing up close to the TV looking down or looking at the TV from an angle (or from the floor looking up). This defect is only seen on a black screen such as a credit roll in a dark room. My newer (12/11, KDL-55HX729 does not have this defect. It's what you can live with. If the TV is within your exchange period, why not return it if it bothers you? I didn't return the 701 because I was lazy and after a while ignored it since I watch this TV from a central position and it seems fine from that vantage point.
Sony KDL-55HX729, Sony STR-DH820 Receiver, Sony BDP-S590 BD Player, Sony SA-W2500 subs, Sony, SS-CN5000 center channel, Sony SS-F6000 left and right front speakers, Sony 3D Glasses: TDG BR-750 & TDG-BR250, Apple TV, APC Back Up UPS XS1500, Apple Airport Extreme.