Top texture of grass blocks turns gray while being pushed by a piston

The top texture of grass blocks turns gray while it's being pushed by a piston. Not much of an effect on gameplay.

Steps to Reproduce:

1. Create a new world
2. Place a piston
3. Place a grass block in front of the piston's face
4. Activate the piston

Observed Results:
The top texture of the grass block turns gray while being pushed.

Expected Results:
The top texture of the grass block should not turn gray.

Video:
20210713_480p.mp4