Items jitter when manually tossed onto ground

Steps to reproduce:
1. Mine up a block and let the item entity spawn naturally. Do not pick it up.
2. Drop an item/block next to the first one.
3. Notice how every 3-4 seconds the tossed item jitters slightly and the naturally spawned item entity does not. The jitter is very minute.
Easier to see if the manual dropped item has edges, like a nether star.