Hello Mojang I've found an error in Minecraft Snapshot 14w30b I have 2x the F5 key is pressed and then I suddenly saw a chunk of was blue!

Hello Mojang I've found an error in Minecraft Snapshot 14w30b I have 2x the F5 key is pressed and then I suddenly saw a chunk of was blue!

What I expected to happen was...:

What actually happened was...:
Describe what happened here

Steps to Reproduce:
1. Put a step by step guide on how to trigger the bug here
2. ...Press 2x F5
3. ...Done!