The bug

When in spectator mode, and entering any entity by left clicking it, while sprinting close to the ground (so the sprint particles are visible), the particles will continue to be created for about 8 blocks.
The fact that spectators can cause these particles is a bug in my opinion.

How to reproduce

1. Spawn an entity, like a villager, preferably with NoAI:true so its easier to hit them
2. Set your game mode to spectator
3. Sprint close to the ground, and adjust the height until the particles are visible
4. Sprint towards the entity, and click it once in range. Sprint towards it from behind, else the particles will not be in your view
   Particles are shown