World generating Bug.

World generating Bug:

I Fly in a Vanilla World in Gamemode 1. But The world Don't generate or Generate very very slowly!
Normaly The World should generate when i fly.

What actually happened was...:
That the World Don't generate, or generate Very slowly!

Steps to Reproduce:
1. You make a new vanilla survival World.
2. You go in Gamemode 1.
3. You Fly around. For example to south.
4. After a few seconds, the World generate very very slowly.