FIXED IN 14w25b - Minecraft 14w18a shader bug black horizon on most shaders.
Fixed in 14w25b.
https://bugs.mojang.com/browse/MC-47513
Most shaders produce a black bar on the horizon when active. GPU is NVIDIA Geforce 660 Ti with driver 337.61, under Windows 8.1 64-bit, using 64-bit Java.
There was a proposed fix, but it was removed because it didn't work 100%. Then an official fix came.