Placing a block downwards while sneaking at a certain height of the world sometimes causes the block to disappear. This is similar to MCPE-22065 but apparently not the same bug, as this doesn't involve a hitbox of moving entities.

Steps to reproduce:

1. Stand on a block at Y=31.
2. Place down another block next to it while sneaking.
3. It should magically disappear. In Survival the block is actually consumed from your inventory, losing the block forever.