I still think it's a bug. The individual camera turns off on the map, but the camera gets lost in the town.
Where is the individual camera defined? - In the hero file for the map.
What happens when a hero hides in a castle? - His model disappears from the map.
I think the hero is removed from the map, but his model and stats are saved in the map's cache, but the path to the individual camera file is not saved.
I don't remember if the hero's icon remains when he's in a boat or in a Sanctuary. Maybe this isn't the same as a castle garrison.