Unfortunately those horizontal lines are real, and they are there. Someone mentioned that if you pause when playing a movie, specially when you have a big object that has only one color, let's say something white, light brown or light blue you can't miss those horizontal lines, and once you see them you will find them anywhere like in scenes when you have a blu sky to mention a few.
It happened to me when I was ready to buy the xbr-55900A and I was watching Toy Story 3 ( in real 3d content....the salesman at Sony Store tried to play only the simulated 3d but I insisted in watching real 3d) and I started seeing those lines specially in all those character's faces like Mr. Potato, of course Woody, etc. Since we saw those lines, we tried a non animated movie to see if those artifacts were due to the animation. We watched The Avengers, and in most of the scenes, because it has a lot of action we could se them a little. but then we forwarded to scene # 16 and .....the lines were there again........try to see Captain America's shield when all the Avengers are together and pause it, you are definitely going to see those lines , it was just like watching throughout a window with blinds or as CNET and other sites described : like a GRID.
Because the guy from Sony and my self couldn't believe what was happening, he suggested to try the 65' tv, and in the big TV those lines were almost invisible, you could see them but if we were watching from a really close distance, like 3 or 4 feet away, of course you are not going to watch any movie from that distance. To be more precise I really couldn't see any lines from a 7 to 8 feet distance. At that point I was a little bit disappointed because I really wanted to like the 3D passive, I still think it's amazing but you have to considered the distance from where you will be watching the movies, which takes a way the fun of watching 3D. I know I am a big fan of 3D, I own a XBR-65 HX950 that uses active 3d glasses and I was thinking about getting the new sony x-9 to enjoy the new lighter and improved 3d passive glasses but due to that experience I thought I should do some more research.
For example those lines are always present if you you watch any 3d content in any LG passive 3d tv with a 1080p, other examples are the new 2013 Sony Tv's : 70" Class (69.5" diag) R550A Series LED Internet TV that uses passive 3d as well......but here we are trying to discuss if you could see those lines in a 4K tv or not.
I found one article from CNET that explains the reason why you see those horizontal artifacts when watching passive 3d but with 1080p, and the same article indicates that 4k should be able to reduce that effect, here is the link:
i still think that passive 3d is the next step in home 3D and I also think that 4K is a huge improvement in High definition, and maybe because Sony has just switched from active 3d to passive 3d it still needs some adjustments....I know that many owners haven't experienced this issues, but since there were some comments about this I just wanted to share the experience that I had with thet new 4K tv's.Edited by DanielMD - 6/22/13 at 10:15am