X and Z coordinates do not match "targeted block" X and Z coordinates, off by one -0 appears as -1

What I expected to happen was...:
I expected that the target block  I am standing on to match X and Z coordinates, while being equal to my Y coordinate minus 1.

What actually happened was...:
The X and Z coordinate do not match up, my "position" doesn't equal the "targeted block" coordinate values, always off by one. It appears to start at the -0, which, according to the "targeted block" coordinates appear as -1 instead.

Steps to Reproduce:
1. start by creating a new world in creative mode, superflat, redstone ready.
2. I'm not sure, sorry, I didn't notice the error until much later, massive changes made to within a 200x20x200 volume area
3. after a few saves and reloads and even changing the thumbnail once, I noticed that the bug started manifesting.