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
Place a torch directly below a block
→ ❌ The particles will collide with the block lower than they should
Alternative method:
Place an always active repeating command block
Enter the following command into the command block:
particle minecraft:smoke ~ ~1 ~
Place another block 2 blocks above the command block
→ ❌ The particles will collide with the block lower than they should
Can confirm in 20w51a. Just for clarification reasons, the particles will not touch the block above them.