Steps to Reproduce:

1. Build a pillar 10 blocks tall.
2. Build another pillar next to that one 10 blocks tall.
3. Place a block one block down from the second pillar poking out.
4. Place sand poking out of the top of the first pillar.
5. Observe that the sand falls sideways when placed, then teleports underneath where it used to be.

Expected Result:

The sand falls straight down.

(DOES NOT HAPPEN ON SUPERFLAT WORLDS)