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.

To Reproduce:
1. Load any world in creative.
2. Visit the Nether.