Right. I found it odd to still be able to fight enemies by playing it after taking out Dragonlord. I had always wondered what would happen, though. My assumption was that the game would tell me nothing happened, same as if I played the harp in a town or Tantegel.
Dragon Warrior for NES: I had wanted to use the Silver Harp in a few scenarios after making the bridge to Charlock and thus used the Treasure Chest editor to add a second harp in another chest. Long story short, any idea why the Harp still summons enemies after the Dragonlord has been defeated and Alefgard is saved? I was eventually able to let a Scorpion kill me and it let me death warp back to the throne room and I went outside for the ending.