When sand or another gravity affected block hits the ground after dropping it from any height where it would fall from, it disappears momentarily then comes back as a regular block. Here is a video: https://www.youtube.com/watch?v=xJeK1piVzM8&feature=youtu.be
Linked issues
Comments 8
If you read the comments of MC-51662 and MC-46225 you'll see the actual bugs don't derive from the piston but from the falling sand; the piston is just a method to induce the behaviour. In the case of MC-46225, sand can fall into a piston, replacing it which effectively destroys the piston. If you add any block under falling sand at the right instant the sand would fall through it, too, if my understanding is correct. I've seen falling sand fall through pistons and then part way into the floor below on 14w10c. It's like it's got acid for blood 😛
My point was there has been recent jiggering (between 1.7.2 and 14w08a) with the falling sand mechanics (which lead to MC-51662 and MC-46225) and this issue may have arisen from that jiggering. How recently did you move to snapshots? Could the issue have been around since earlier snapshots and you didn't notice until recently? There has been subsequent jiggering which has evolved MC-51662 and MC-46225 over time. This is likely the changes to the tick processing for block updates, or other recoding around the Mojang's efforts at making MC more efficient.
Falling sand is a different object to sand at rest, IIRC, so there may have been other code changed recently that's delaying the transition from falling sand to stationary sand. Is the behaviour the same for gravel and all other gravity affected blocks? Just wondering if it's a property of the falling mechanic or of sand itself.
Most likely a duplicate of MC-62552
Daniel, double check the numbers again. This one is lower than the other one. Also, that one is about the block mid-fall, and this is not just about sand, but it also happens to gravel and anvils.
Related to MC-51662 or MC-46225?