I was in my survival world. I always run the latest snapshot and had visited the Nether in 14w25a without problem. However, as I started to explore newer chunks that I had never loaded, there were huge gaps of air that ran across the Z axis. Only the bedrock floor and celling generated. As it turned out only every other chunk on the Z-axis had loaded. Also, the terrain generation is completely messed up, with huge netherrack walls.
Then, I re-created the world in creative, and found the whole Nether distorted, which proves that this glitch is new to 14w26b. I found a Nether Fortress, but it had generated fine.
The same glitch applies to the End. Also, the obsidian pillars do not generate in the end.
1. Load any world in creative.
2. Visit the Nether.
MC-58975 Nether generates in strips if it doesn't crash