When a group of falling blocks (concrete powder, sand, etc.) fall, some will break when upon landing on each other. The expected result is for them to stack up normally without breaking, Falling blocks will also unexpectedly break when the platform beneath them retracts via pistons. I have included two videos, showcasing the unexpected braking when they land, and the other showing breaking by retraction.

Edit: The two videos exceeded the 10 MB file limit. If there are any authorized 3rd party websites to upload the videos to, let me know. Thanks!