When I create command summoning three falling sands (one on another) then third falling sand is turning into a item.
Command:

/summon FallingSand ~ ~3 ~ {Time:1,Block:"stone",Passengers:[{id:"FallingSand",Time:1,Block:"redstone_block"},{id:"FallingSand",Time:1,Block:"quartz_block"}]}

On screenshot is shows moment with item whith should be a falling sand.
(Sorry for my bad English)