Shulkers' projectiles get confused if on a wall

When on a wall, a Shulker I was fighting shot some projectiles that didn't follow normal projectile movement patterns and went in a diagonal in a random direction.

I expected that the projectile would move normally and hit me while traveling on the normal axes

But, instead, when shot from a Shulker on a wall, it started going diagonally off in a random direction.

Reproduce:
1: Find an end city.
2: Find a Shulker on a wall.
3: Make it angry. It will sometimes shoot it's projectile in the way explained above.