Your Now Playing should preserve the last thing that you selected to play. If it was a shuffled playlist, that shuffled playlist should still be there in the order in which it was playing when you closed MB cued to the next song.
The exception would be if you have "Edit->Edit Preferences->Now Playing->clear playing tracks and current playing track on restart" turned on. This would negate the behavior you're looking for.
If you want Now Playing to remove the songs you've already listened to, you can set that in Edit->Edit Preferences->Now Playing->prune played tracks