Being that I work for a company owned by Andersen Corporation, maker of Andersen Windows, I've heard through the grapevine about windows concentrating and reflecting sunlight onto neighboring houses and in many cases causing damage. (Sorry, I don't have any inside knowledge or access to damaging "internal memos" or any other smoking guns that a class-action attorney would sell out his best hunting dog for. If any lawyers are reading this, go subpoena sumebody else.) Plastics News had a article on it recently, but this has been going on for a few years.
What is thought to occur is that with a sealed, double-paned window, pressure differences between the sealed interior and the exterior can give the window glass a concave geometry of sorts, which can then serve to concentrate sunlight. Low-E glass is particularly troublesome in this regards. The reflected and concentrated sunlight can then heat and soften vinyl siding on neighboring houses.
I'd love to run a Monte Carlo simulation on this sometime to see how it plays out. Or maybe a derivation of the Drake equation would be better. Think about what has to work out just right for this to occur. First the right pressure differential has to be there, not an easy set up to control. External atmospheric pressure is constantly changing as is the pressure inside the window due to changes in temperature. Then once you have the concavity, you have to have sunlight. And then the 3-D geometry of the sun, window and neighboring house has to be just right. And then the focal length of the lens has to match (not exactly, but close enough) the distance to the siding. My gut feeling is that this would be a "one-in-a-million" type problem, comparable to winning the lottery, but apparently not.