After reading this post:
I took a closer look at this image(48MB TIFF):
After messing with levels and looking at the blue and green channels by themselves there is a noticeable change in the texture of noise in the sky between the top half and bottom half of the picture.
The change happens exactly(to the pixel) in the middle of the picture and is visible on both sides of the car.
To me it looks like that the top half of the image and the bottom half are being compressed independently of each other. It is probably much more apparent on images like this one where the top half and bottom half are very different.
I wonder if this is baked into the hardware of if it is something that could be changed with different firmware.