When you teleport outside the border, then come back in, commands stop working entirely. /tp, /setblock, etc won't do anything. This happened when I teleported to the border for no reason other than to see it for myself on a world (Creative of course.)

Steps to Reproduce:

Create a new world

/tp loverminecraft/yourplayername 100000000 56 100000000

Try to use /kill or /tp

You are now officially stuck forever

This could mean that Minecraft broke though, no idea.