Mariner's Vengeance bug

A friend of me was playing Mordekaiser this afternoon and I think we found out about a bug with the new item in Butcher's Bridge. When Mordekaiser his ghost of a champion with Mariner's Vengeance dies, he still gets the unique effect from this item and gets invulnerable even though it's just the ghost of Mordekaiser. Does this work as intended?