HoMM3 HD is a mod (add-on) for the game Heroes of Might and Magic 3.

Well, there's no doubt that this is a bug, so it's already causing problems just by existing. :)

All I can say is that baratorch could have included a fix for the neutral unit pathing issue in the same release, but he chose not to.

In any case, the website clearly states:

ATTENTION! HD+ changes the original rules and possibilities of the game, so if, for example, you are playing an offline tournament on a clean SoD/Complete version, you must disable this option.