it happens
motion disabled sand
do not destroy one piece of sand
chain reaction of falling
Nope.
That's exactly what I did.
I broke a sand block underneath it, and it all fell down.
Once Minecraft had successfully lagged for 20 minutes, and crashed once or twice, that was the outcome.
No matter what I do, that sand doesn't fall.
I was working around that area, and a creeper came and blew up a chunk in the sand.
I repaired it all, no problem, not a single block had fallen.