Video: https://youtu.be/qAZFB5zvpjo

When shifting, you can go back different amounts.

How to reproduce:

step 1: crouch at the end of a block. Check your coordinates.

step 2: move up a bit, then move back, still crouching. Your coordinate is different! :o

I find this kind of strange, but whatever. It just means that players are differently spaced out.