Occasionally, after picking up an item entity spawned from breaking a block located above air, the item will appear to reappear in the same location as it originally formed, fall, rest on the ground for a moment, disappear, and restart the cycle again. This is entirely visual, and the ghost items do not appear to be capable of being interacted with. Updating blocks in the area seems to stop that item from being respawned.
Tested on singleplayer only, and not with blocks destroyed by explosives.