Howling Abyss and Wicked Hatchet

On Howling Abyss, The Lightbringer is available to purchase but you are unable to build it's component Wicked Hatchet. While you are still able to build Cloak of Agility and Lightbringer in full, if you lack the necessary gold to build it you cannot purchase both the components.

Simply put, Wicked Hatchet need's to be enabled for purchase on the map.