Grass spawning on sand

Steps to reproduce : 

1) Create a new world

2)Travel to a place where the sand is near the grass blocks 

3) Observe the sand blocks

Observed results:

Grass spawns on top of sand

Expected results:

Grass should not spawn on sand

NOTE:

An intresting observation is that although the grass renders on top of the sand , after few seconds the game realizes that it shouldn't happen and breaks the grass.