Items and tools appear to float in midair after the player dies, they cannot be picked up, but still despawn normally. Appears to happen when I die to hostile mobs, so that's how to recreate it. The below screenshot is my items after being blown up by a creeper, but I've also had it happen with zombies, skeletons, etc. Also I was playing in survival mode. Placing blocks, then standing on them to become at level with the items does not work, nor does mining the blocks beneath them.