I found this painful bug the hard way.
If you load a music file into osu while that specific music file is in use, and that music file is being attempted to be overwritten, it will fail to move that file and place that song into the Songs folder instead. If you then delete that while that song is still in the Songs folder, your entire song folder is deleted.
This means that I will have to download all the songs again for finding this.
This applies to any song that is 'stuck' in the Songs folder.
If you load a music file into osu while that specific music file is in use, and that music file is being attempted to be overwritten, it will fail to move that file and place that song into the Songs folder instead. If you then delete that while that song is still in the Songs folder, your entire song folder is deleted.
This means that I will have to download all the songs again for finding this.
This applies to any song that is 'stuck' in the Songs folder.