Playlists get mixed

Although I am pretty fastidious about creating and using playlists it seems that periodically the contents of playlist get randomly mixed. For example yesterday I was browsing a playlist titled Nu Disco and discovered that virtually the whole contents of another playlist titled Jazz had been mixed in with the Nu Disco playlist. I understand that I can make regular copies of my playlists so that I can revert to originals but want to know if there is anything I can do to prevent this happening. On another thread I noticed that someone else mentioned this problem but there was no solution. Are others having a similar problem?