Manually editing M3U - changes not reflected in LMS

I have manually edited a playlist created in LMS 7.9.0 (Windows 2008 Server), but I can't get the changes to the playlist to take effect in LMS. When I open the playlist in the LMS web interface I only see the original (un-edited) version. My playlist folder is set to C:\Users\my user\Music\Playlists, which is where the edited playlist file resides. I edited the M3U using Notepad++
I've tried restarting LMS Server, and also a library re-scan, but still I only see the old playlist contents.
Any ideas??