When the Halloween texture pack is applied, the panorama is changed to the Halloween mashup world. However, the world is in the Halo texture pack instead of the Halloween one! I have no idea how this mistake was made, but it's quite obvious once you notice it. The biggest giveaway is the purple wood and spartan helmet pumpkins.

To Reproduce

Apply the Halloween texture pack as a Global Resource. Then, the default menu should become orange, and the background panorama will change. The panorama is using the Halo textures in the Halloween world.