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

Just to clarify: the absence of necromancy is not a bug; the absence of navigation is definitely unknown: it's possible that it was intentionally disabled, but I think it's more likely that it was a mistake and they should have disabled leadership instead, as is the default on fixed maps.
However, the absence of all other missing skills – skills with numbers greater than 15: water magic, earth magic, literacy, tactics, artillery, learning, attack, armor, intelligence, magic, resistance, first aid – is definitely a bug.