When I've generaded a new world (survival, worldtype:custom), the world was generated correctly around me to about 10 chunks.

If I was walking ahead any horizontal direction, after few hunderts blocks, there was no visible ground (grass, anything). I could walk further stepping on nothing. The underground structures was visible through this void. Few blocks further there was visible ground again. On plains the bands of invisible ground was visible. After reloading world, the ground was visible again, but if i have walked again, the invisible ground have appeared in another place.

This bug makes game unplayable!

Steps to Reproduce:
1. Generate new world
2. Walk ahead in any direction
3. Enjoy transparent ground of undisplayed blocks/chunks