This is easy to replicate:

Make any new world - preferably creative - and then teleport to to edge of the world:

/tp @p 30000000 100 30000000

Then, use the following command to place a layer of sand in the air next to you:

/fill ~1 ~1 ~1 ~15 ~1 ~15 sand

...and watch them as they horrendously glitch out and go crazy until they land.

Also, I'm not 100% sure, but it does seem as if it takes them longer to reach the ground as well.