A big hole in the ground !

Playing in Creative mode, Cheats ON. Started a new world and was flying around for a while (about 15 minutes of real time), when I came across a big rectangular hole at approx 1130, 63, -2374. Stars are visible through the hole, and mobs can be seen in a cave. It is not possible to drop into the hole.

The game directory is too big to attach (approx 40 Mb).

Exiting MC and reloading the world cleared the glitch.