When shearing a sheep, the wool items created will stutter while flying. This is not the case when shearing mooshrooms or performing other actions which create item entities.

According to haykam, the sheep-shearing code has its own unique implementation which adds a velocity to the created item(s). It seems like the client isn't fully on board with this and assumes that the item is created with a little pop of motion, as dropped items usually are. Changing the sheep code to work like the mooshroom code should fix this.