Extreme lag when happy ghast passes through scaffolding

Gave happy ghast a harness and bound it with a lead to a fence post. A block or two from the fence post is a tall column of scaffolding. When the ghast passes through the scaffolding it causes extreme lag: mobs slow movement and stutter in a slide-show fashion when they do move, eating is slow or not possible, damage from fire slows - anywhere in the world, not just near the ghast. When the ghast passes out of the scaffolding, lag stops and all described activities return to normal.