Parent map only works if it's in the same "branch."

[]World Map
|____[]Hyper Town
[]Moon
|____[]Super Town
|____[]Cheese Town
|____[]Ramen Noodles Land
.........|_____[]Soup Arena

For example, if Hyper Town is set to "parent map" for music, It'll have the same as World Map. It doesn't matter if you got there from Ramen Noodles Land, it'll just have the same as World Map. Soup Arena would have the same as Ramen Noodles Land.