Noticed while placing torches above me and mining diamonds.

Steps to reproduce:

• Place a torch directly above you, 2 or 3 blocks high.
• Break the torch, so the item would fall behind you.
• The item is gone.

It seems when the item falls behind the player's model, it disappears into the void.

Happened while mining as well, if a mined diamond is falling behind you, it disappears.