There seems to be a bug with the playlist function in that you can't open a playlist & then resave it under the same name. If you open an older playlist & make changes, you must rename it something else when your save it. I suspect that's why there's a Save As ... option instead of a Save option.

I only became aware of this issue 2-3 weeks ago. And I tested it out & as suggested, saving under the same name will result in a corrupted playlist.