Okay, then...

GooseGog... Do you have any playlists tagged as "Ignore As Child"? That would explain your observed behavior, too.

If this is the problem you are experiencing, then it's "by design". When you press down-down-down on the front panel, it plays the root playlist and all of its sub children, except those tagged "ignore as child", those filtered out by a Wendy, or tracks not existing in playlists. So playing the "entire playlist tree" might not play every song on the player.