"Running" while flying through blocks in spectator mode will cause spawning particles

As the heading says, particles get summoned when you are in Spectatormode and "run" through blocks. See screenshot

Steps to reproduce:

1 Make a world that has enough blocks to fly through without any gaps. The superflat template "Tunnelers' Dream" is recommended.

2 Run the command /gamemode 3

3 Fly through the blocks while pressing the "Run-Button"
(in Default Setting it's [Ctrl])

4 Try to look behind you while flying