You can fall through bedrock in superflat

For some reason after following these steps you can fall through the ground upon reopening your world.

Steps to reproduce

• Create a superflat world.
• Dig down 3 blocks. (you should see bedrock.)
• Go into the hole and look up.
• Reopen your world.

When the world is reopened, you will fall through the ground. This also affects survival in superflat because when you reopen your world you die!