The player X and Z coordinates in the F3 screen are not the same as the X and Z coordinates from the 'looking at block/liquid', when looking to a block straight below the player.
This is only the case with negative X and Z coordinates, as the 'looking at block/liquid' skips the -0 and jumps straight to -1.
The coordinates from "looking at block" are rounded because the coordinates of the blocks are integer values.