Items disappear and reappear above from mined section.

I go mining a lot,and during the 1.8 snapshots,I've noticed that when some items get left behind in the shaft/quarry branch,they manage to somehow make their way above ground.

HOW TO RECREATE:
Mine underground,or under another block,
item will disappear,such as it looks when decaying,
item appears above ground,or block.