I was attacked by a navy brig. When the instance loaded the ship had no captain and no name something like "shipname", no crew, and no flag. The flag and rigging were totally white with no rendered textures.
Cool, free brig to capture right.... wrong. The ship had no collision and did not move, I could sail right through it.
However I could not leave the battle and after a while noticed that my hull armor was being damaged. It was like there was an invisible npc ship somewhere hitting me. I had to sail away for about 10 minutes before I was able to leave the battle.
(submitted an F11 report)
Also: There was an instance where I joined a battle to help a fellow Frenchman out. It was him in a snow pitted against an AI Navy Brig and Privateer (I think). Well the guy who started the battle decided to run and the privateer gave chase. I engaged with the brig and was soon joined by another French Captain. We sunk the brig and started to look around for the remaining ship. This privateer was barely visible on horizon in the battle instance (still chasing the snow who left the battle 10 minutes earlier). There was no way for us to catch him and he was just sailing straight still focused on a ship that had left the battle. So we had to leave the battle leaving the AI ship to sail off into the abyss.
It seems AI will stay focused on a player even if he leaves the battle and keep chasing a "ghost ship"
(submitted F11 report)