Strange. I just clicked on 6 or 8 different playlists, in the Left Navigation Area, and each time it showed the playlist and the summary at the bottom showed the number of files, total size, and total time.
If you can't get this to work after restarting MC, maybe it would help you to know that Control-a is MC's select all key. So you can just click on any song in the list, then press control-a to select all of them.
Good luck.
Brian.