This is not a bug, those squares should not be visible Line of Sight works by drawing a straight line from the center of your square to the center of thet target´s square. If no blocking terrain or otherwise (Wall of Illusion) is in the way, you have sight of that square. This means that some squares might not be visible, but square PAST them can because of how isometric diagonals work and this is why we sometimes have skewed line of sights. If you try to draw a diagonal to the right X, you´ll notice the right blocking rock denies you, if you try to draw to the left, you notice the left rock also blocks you. But if you go past them and towards the goblin, your line goes straight through the chokepoint and directly through your target. Just imagine that in first person: You´d see a very narrow hallway from there, and a goblin standing straight in the middle, but you wouldn´t see the handsome rogues hiding behind the corners, would you?
