When a player is falling and hits the side of the block, depending on the situation they can actually land on top of that block.

How to reproduce:

1. Place one block at least 2 blocks off the ground, then place another one block lower than the first with a two block gap in between.

2. Face about straight forward, and sprint directly off the block.

Or:

1. Place one block at least 2 blocks of the ground, then place another one block lower tan the first with a three block gap in between

2. Face about straight forward, then walk forward and jump at the last second

Note: This works without Auto-Jump turned on