When placing sand/gravel/anvil/dragon egg that it would fall down the summoned fallingsand entity glitches out:

• wiggles strangely
• Is partly invisible

For a more detailed look, watch: https://youtu.be/GWCV5T6ejs0

Testing was done in a DEFAULT world generated with the 16w39c snapshot

The (primed)tnt entity on the other hand behaves completely normal (as it is a completely different entity after all.)