I tried:
/summon FallingSand ~ ~-2 ~ {TileID:1,Time:1}
But i didn't find any "falling sand" until it reached the ground and solidified.
The command executed > I see nothing happens > wait a few seconds > the solid block will appear in the spot where the falling sand should have fell
Falling sand is not showing up VISUALLY.
I have this too. Unfortunately, it has not been fixed and is brought back in Minecraft 15w34d 1.9 snapshot. It works for a little while after I load up the world, but then it stops showing.