Mobs can pick up items on their death and destroy them that way (including their own drops)

Dying mobs can destroy items

When a mob that can collect item dies it first drops some loot, but still can collect items afterwards.
Those items won't get a chance to be dropped again and just vanish. This includes the mobs own (rare) drops!

Steps to reproduce:
1. Find a mob that can collect items
2. Kill it in a way that it will be in range of some items (or his own loot)
3. Notice how it collects the items (the "dead" mob holds them) and disappears

Video showing the process: http://www.youtube.com/watch?v=cSFhVL_ES3M