Falling Sand (or any gravity-affected block):

-CAN land on these blocks, if it is dropped by your character.

-CAN'T land on these blocks, if it is spawned from a spawner.
-CAN'T land on these blocks, if it is dropped by your character, and you quickly log out and log back in.

-soul sand
-beds
-cactus
-chest
-enchantment table
-ender chest
-end portal frame
-hopper
-bed
-cauldron
-player heads

Check gif below for example.