The Bug

Unlike falling on north-west, east-south edges cause falling blocks drop corresponded items instead of placing above blocks.

How to Reproduce

1. Place a stone on ground (surrounded with air :

   /fill -1 -1 -1 1 -1 1 stone
   /fill -1 0 -1 1 0 1 air
   /setblock 0 0 0 stone
   

2. Summon a falling sand above it with x or z offest 0.5:

   /summon falling_block 1.0 2.0 1.0
   

Expected Behavior:

The falling sand turned to block above that stone.

Observed Behavior:

The falling sand dropped its item.

Note that this doesn't happen if x and z both offest -0.5:

/summon falling_block 0.0 2.0 0.0

but still if quite exceed:

/summon falling_block -0.1 2.0 -0.1