So my party entered King Boreas' room via the door with the password scroll. When the door opened, we saw Boreas straight ahead, so we came into the room, hasted Madora, and went charging into battle as we usually do. Madora missed, but was not in combat for some reason. The rest of us then walked up the stairs and were able to just pelt Boreas with attacks while he continued to walk in a slow circle like he was when we entered the room.
Killing him gave us credit in our quest log, but we're worried that killing a major boss in such a bugged way may cause bad things to happen later. Has this happened to anyone else?