map editor mirror bug

so tested this bug and try to find out mathmaticly whats wrong here
now stick with me, ill try to explain as easy as possible

ill post a vid too:

so basicly what happens here is you mirror the top to bottom (or any other direction for that matter but lets stick with this for easy explaining)

i just created underlord 1 and 2 located like so

1 | 2

now logicly if i mirror the map it should be like this:
1 | 2
_____
4 | 3

this would be a perfect mirror (seeing how when looking into a mirror left ir right and right is left)
however i just keeps counting like regular
1 | 2
___
3 | 4

this is not mirror, further more it does not spawn the 4th underlord

i hope this makes sense if not ill elaborate