The bug:

If you start mining an item from a suspect gravel/sand, once you stop mining it, gravity will not affect the block until the item is hidden in the block.

Steps to reproduce:

1. place a block, and put a block of suspicious sand/gravel on top of it with the item in the block
2. start extracting an item from a suspicious block
3. stop extracting item from suspicious block
4. destroy the block on which the suspect block is located
5. suspicious sand/gravel does not fall until the item is hidden in it

Expected behavior:

When an item is no longer being mined from a suspicious sand/gravel block, the block should drop immediately after mining is complete.