Sheeps being sheared don't change the appearance to "sheared sheep"

Sheeps being sheared don't change the appearance to "sheared sheep".

This happened when I sheared sheeps to collect wool. The sheep didn't change it's "surface feature" as the picture shows.

(I'm sure this sheep have just been sheared. After being sheared it cannot be sheared unless it eat some grass from grass block)

Sometimes the oppposite thing happen, a sheep with the appearance of "sheared sheep" can be sheared by scissor. I'm sure it is a skin error take place when the surface need to be changed.

Only if I reload the chunk where the sheep stay can it change the surface