Board Thread:Wiki Discussion/@comment-35301431-20140327204149/@comment-12633677-20140522182529

Okay. Category:Collaborative songs shouldn't have any song pages in it. Neither should the categories the next level down, which are Category:Group rendition songs, Category: Trios songs, and Category:Duet songs. This leaves the very lowest level of categories (e.g. Category: Chinese duet songs and Category:Japanese trios songs), which is where the song articles do belong.

This is because, to quote Wikipedia, "Normally articles should not appear both in a category and a 'parent' of that category".

Hopefully that makes sense? *_*