I was throwing items out onto the ground with expectations that my inventory would pick up the things I spawned in or when my inventory was full, leave them on the ground to wait for a new slot as I was putting them into a chest.
But upon doing so, the top row of my inventory stayed empty and continued to pick up the items on the ground, deleting each as it was taken. I thought I was just being stupid with getting the things I wanted. I then later broke a full double chest to find my inventory picked them ALL up, but all that couldn't fit into the slots, it deleted.

Steps to Reproduce:
1. Enter game on super flat world(creative).
2. Go within the range of a beacon on a full diamond pyramid with speed 2 locked in.
3. Proceed to spawn in items and picking them up(I was doing leather armor because they don't stack).
3B. Break chest full of items and pick up dropped items.