The X/Y/Z co-ords do not include -0 in the F3 screen, whilst they do in the minecraft world. This means that all negative co-ordinates in the debug screen are one less than they should be. This causes trouble whilst dealing with command blocks, as negative absoloute coordinates are incorrect.
WAI. This is the moderator note from MC-36602:
Moderator Note:
This is working as intended as there is no +0 and -0 coordinate as that violates the laws of math, 0 itself cannot be positive or negative only coordinates greater or less than 0.