The bug means that whenever the player has a block fall on just their feet, they will just fall through the floor indefinitely until they reach an air gap

What I expected to happen was...:                                                                                               When gravel falls on me underground, I will stay in the block and be able to mine through it

What actually happened was...:
As soon as I was submerged in gravel, I was shoved through the floor, into the void

Steps to Reproduce:
1. Create a room where the player cannot move horizontally at all, so maybe place 1 block high barriers around player
2.Drop a block of gravel or sand on the player