I also took the chest to camp, so I could get astarion to pick it open and took out the bottle. Then kicked him and went back to the cave and killed the spectator. That happened just before the first instance of the bug - So I can see the link. But 2nd instance not so much: i did exactly the same and it didn't bug, yet now a day later it has bugged out on that save, much further down the line, messing around in the druid grove.