Summon FallingSand Despawns

Whenever spawn a falling sand with the summon command, it shows for a second and despawns instantly, whether it's inside a block, on a block, or in mid-air. This is what I am typing:
/summon FallingSand
I also tried using a command block to do it, and that didn't work either, even though I typed:
/summon FallingSand ~ ~-2 ~
Please fix this bug; it is very annoying.
P.S.
I also tried
/summon FallingSand ~ ~-2 ~

{TileID:11}