Hitboxes don't rotate with entities. This causes lots of inaccuracies, especially with entity collision re-added:

• Shooting arrows near a mob will hit it incorrectly if it's rotated
• Attacking near a mob while rotated will hit the mob
• Walking near the edge of a rotated mob will cause you to collide with it
• The Elytra may collide with blocks when the player is rotated

The first screenshot depicts the hitbox while rotated.

The second shows how the player collides with the sheep, even from the edge.