When an item drops near a wall, it may phase into it, causing the entity to glitch in the positive y direction to the first air block it contacts.
I come back up from mining a shaft, and there's uncollected cobblestone and diamonds laying everywhere around my base...
Duplicate of MC-47650 - If you have not, please use the search function in the future, to see if your bug has already been submitted. If you could not find the original report, please comment with the keywords you searched for.