Dr. Cyanos' Lootable Bodies
With "Drop as Block on Death" enabled, the backpack will spawn next to the corpse, but a duplicated backpack will be in the corpse's inventory.

With it disabled, the items in the backpack can be destroyed if their inventory doesn't have enough room for its contents.

This doesn't seem to be a problem in the latest version. If it re-occurs, please reproduce with 3.1.3.