World crash then spasms on loading screen

I was typing in a /fill command and deleted a character, when the screen froze for ~2 minutes, then the screen went to the mojang loading screen and started spasming until I alt+f4ed minecraft

What I expected to happen was...:
The character to delete and me to continue playing

What actually happened was...:
Screen froze, world crashed, mojang loading screen started to spasm, then game audio could still be heard.

Steps to Reproduce:
1. I have no idea how to reproduce this
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