Stefan Tanja

Not building level, building level is still on the positive y-axis. Going below y=0 with F3 opened, or pressed F3, then the game will crash. This happens for any world you have.

@kumasasa it will be unfair for players to lose all of their equipment just because they accidently shot an ender pearl through the barrier, and because of the damage being dealt they will lose their equipment.
It would be better if you just could be teleported to the closest block of air from the world border after you teleported. For example: the world border is at (50,20+1,40) and you teleport to (60,10+1,40) - the wolrd border is directly in your back and the "+1" comes from the block of air. After you teleported, you will be teleported to (50,20+1,40), thus not losing any items. It would be nice if this could be a possible solution, but if it is impossible then I guess you shouldn't cross the world border with any valueable items in your inventory.