The bug
When landing on a block with a collision box higher than one block (walls or fences) the landing particles shown are those of the non-full block above. If there is no non-full block above the fence/wall then the correct particles will be shown.
How to reproduce
Place a fence with a torch on top
Land on the fence
→ ❌ The landing particles shown are those of the torch
Note 1: This glitch has probably been around for longer than just 1.12, but I dunno
Note 2: Yes, I did search. If this has already been reported, then sorry 'bout that, but I did my best to make sure I wasn't making a duplicate.