Items dropped after a big explosion float in the air

When you blow up tnt from Y:1 to Y:255 from the top, and you wait for it to explode, there are some stone and dirt items floating in the air.
To replicate:
1.do /fill ~1 1 ~ ~1 255 ~ tnt
2. light the tnt at Y:255 from a side, not the top.
3. wait for it to explode.
4.go down and look at the damage.
You may see this: