/worldborder set slowly even kills you when inside

What I expected to happen was that when I did the /worldborder set 50 600 (from /worldborder set 500) it would slowly bring the border to 50 from the center without killing me.
What actually happened was that when I tested in survival I was being killed and everything else was too. (I was inside of the border)
Steps to Reproduce:
1.Do the /worldborder center ~ ~ command
2.Do the /worldborder set 500 command
3.Do the /worldborder set 50 600 command
4.If not already switch gamemode to 0