When using a command i.e. /fill, setting x or z coordinates as -0, places the block on 0. Likewise, any coordinate with a negative number will register as one block closer to 0 than it should be.

The commands are clearly not counting -0 as a number. You need to either remove -0 from the coordinate system or add -0 to the command system.

Personally, I don't think 0 or -0 should even be coordinates since 0 denotes nothing and weather you are on block 1 or -1 you have one block. You can't have a line 0 blocks.