Killing a mob being ridden by an item creates an unretrievable item

What I expected to happen
I would be able to pick up the item after the mob was dead, since summoning an item (/summon Item) allows me to do so.

What actually happened
I couldn't pick up the items, nor they were gone. They just stayed above the ground, and I couldn't pick them up, even though my inventory wasn't full.

Steps to Reproduce
1. Execute this command:

/summon Silverfish ~ ~1 ~ {Riding:{id:Item,Item:{id:1}}}

2. Kill the mob
3. Try to pick up the dropped item. You won't be able to.