Weird behavior at high X/Z coordinates ("far lands").

I teleported myself to X:10000000 using an external app, and when I got there the following things happened.

1. I feel through the world (I was expecting this)
2. I couldn't place blocks
3. When I tried breaking blocks the hitboxes were weird, if you are able to reproduce the bug you'll be able to see what I mean.
4. I couldn't move North or South, but I could move East and West.
5. Animals would spawn and instantly fall into the void.

I should also mention this was a superflat world.

Steps to reproduce:
1. Generate a new superflat world. (This is what I used in my test, though a normal worlds may do the same thing).
2. Get pocketinvedit or any other tool that lets you teleport.
3. Teleport to X:10000000
4. You should see the issues mentioned.

This could be fixed by preventing players from passing a certain place in the world, like PC's world border at 29m blocks.