The bug

Smoke particles that come from torches or are made with the /particle command hit the block on top of them 0.2 blocks lower than they should. 

To reproduce

1. Place a torch directly below a block
   → The particles will collide with the block lower than they should

Alternative method:

1. Place an always active repeating command block
2. Enter the following command into the command block:

   particle minecraft:smoke ~ ~1 ~

3. Place another block 2 blocks above the command block
   → The particles will collide with the block lower than they should