The Bug

Changing the 'BlockState' value of a falling block with commands doesn't update client-side (doesn't visually update) causing the block that's falling not actually be the block that lands. see attached video.

NOTE: Reloading the world/relogging updates the appearance of the block. 

Steps to reproduce

1. Put 2 command blocks next to each other
2. Put this command in the first one: /summon minecraft:falling_block ~ ~1 ~ {Time:1,NoGravity:1b}
3. Put this command in the second one: /data merge entity @e[type=minecraft:falling_block,limit=1,sort=nearest] {BlockState:{Name:"minecraft:gravel"}}
4. Power the first command block, then the second one.
5.        Notice how the block doesn't visually change.
6. Run this command: /data merge entity @e[type=minecraft:falling_block,limit=1,sort=nearest] {NoGravity:0b}
7.        Notice how the block changes to the correct one only on landing.