Items become detached from their sprite. The sprite moves around while the item stays in a particular place.

How to replicate:

• use an anvil to rename a nametag to "Jeff"
• use a command block, set it to repeat mode, and place a constant power source beside it
• use /execute command to fill in the block that "Jeff" is occupying {/execute @e(name="Jeff") ~~~ fill ~~~ ~~~ glass 0 keep}
• throw nametag "Jeff" out of your inventory from high above the ground, then back away from where you are very quickly
• if it works, some glass should be placed in the air in front of where you were, but the nametag will fall to the ground with no glass getting placed around it, and trying to pick it up does nothing
• if you fly back up to the glass that was placed, you can pick up the nametags and the sprite will disappear from the floor, no matter how far away

This issue can glitch can occur in other, more natural ways, this is just the easiest method to reproduce it.