Grass blocks under hoppers turn into dirt blocks

Summary:
When a hopper is placed on top of a grass block, the grass block will turn into a dirt block after some time.

Steps to Reproduce:

1. Place down a hopper on a grass block
2. /gamerule randomtickspeed 1000

Observed Results:
The grass block turns into a dirt block.

Expected Results:
The grass block should not turn into a dirt block.