Some random terrain was made on a new super flat world. I have a screen shot .png to show you.

Remake this! You didn't write your system SPECS, or a description.

Also, that is because of a chuck error or something. You know how in normal worlds, you sometimes have chuncks that are not there? Well, this could be the opposite, I suppose. :I

Are you SURE you created this world in 1.4.2 pre? This only happens when you flip from 1.1 to later versions (to my knowledge).

Also, you did not write a description. How do you expect people to help you?

I agree with ZeHelper.

I once made a world in 12w42a, and when I converted it to 1.3.2, Something SIMILAR happened.

Happens when level.dat becomes corrupt/updating a flat map to a newer version of the game

This can also happen if you have recently deleted a world with the same name as your newly created one. The game hasn't deleted all the old world files and some chunks from the old world are put in the new world.

Duplicate of MC-315?