Falling block placing at Y=1 changes into dropped item when landing on Y=0

The Bug
If you place a block which needs support below (e.g. sand, gravel, anvil, dragon egg and scaffolding) at the altitude Y=1 without supporting below, let it fall just 1 block and land on the altitude Y=0, it turns into an item instead of a block.

How to Reproduce

1. Create a world in the current snapshot
2. Go to the altitude Y=0
3. Place such a block at Y=1
4. When it lands on Y=0, you will notice that it turns into a dropped item