You need to rescan for Playlists to be added under the Playlists > Imported Playlists node in the Media Tree.

I've save a playllist .m3u file from MMW4 to my HD and then File | Open URL or File ... in MMW5 thinking the playlist would show up on my PlayLists sub directory. MMW5 thinks about it for a while but I have no idea if it the playlist was imported or where it went if it was. I don't want to mess with the actual mp3 files, just the playlisit.