The Disappearing Playlist

I hope someone can help so this doesn't happen again.

I don't use playlists too often. I spent some time creating a special playlist.
I was able to edit it and add to it. It appeared in the Playlist folder under My Music.
I played it many times. While working on it I tried to find the actual file. It wasn't in the designated playlist folder with the other playlists. Searching the system for the file by file name turned up nothing. The playlist continued to be available for playing and editing.

Until,

I did some tag updates and needed to do a rescan. I did the Clear Library and Rescan Everything scan.

The playlist is gone. Other playlists contained in the Playlist folder remain available.

What did I do wrong? Why wasn't the playlist saved in the playlist folder?
How can I ensure that in the future playlists are saved properly?

Thank you,