Falling Sand Despawning

I was messing around with Falling Sand on riding entities and it seems that it despawns after a certain amount of time?

Steps to Reproduce:
1. Enter
/summon FallingSand ~ ~ ~ {TileID:1,Time:1,Riding:{id:WitherSkull,direction:[]}}

OR

/summon FallingSand ~ ~ ~ {TileID:1,Time:1,Riding:{id:ArmorStand,NoGravity:1}}

(Do commands in the air so the sand doesn't land)

After about a minute the sand will despawn.