When you summon an armor stand with a passenger, a falling block, and you destroy the armorstand, the block falss. If you summon them on the same spot again, the second block falls on top of it. The lowest block then turns into a ghost block. 

https://youtu.be/csgWO41RmwM

Command to reproduce:

/summon minecraft:armor_stand 14 4 12 {Passengers:[{id:"falling_block",BlockState:{Name:"sand"},Time:1}]}