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

There's no need to talk about the clone bug; if it doesn't happen, no one will notice (I don't really know what this bug is, clones aren't used often in online games).

But if it does happen, everyone will notice! :) Because this bug happens with 2-hex units. It involves the clone partially overlapping the original, becoming invisible (but impossible to destroy!), and then causing the game to crash! :( This has happened to me several times, and it's a very unpleasant thing in difficult battles.
By the way, Sav wrote about this the other day on df2:

the check for a free hex for the stack includes considering the hex under itself as free, which was one of the reasons for the bug with cloning two-hex creatures.