In the latest version of Minecraft 13w39a, the shader, minecraft:shaders/post/art.json shows a black screen, which I believe is an error in the shade, for this did not happen in 13w38c.
I have added a screenshot from 13w38c, which the image is clear, and I added a screenshot from 13w39a, which appears with black text, when for my screen it is actually all black and it is unable to see anything.