Glitch Spectating mode and particles

While in-game, it's possible to spectate the game and nobody would noticed even there's a player spectating.

About an hour ago, i noticed that sometimes i could "hit" someone that was spectating, i first thought "This maybe because he asked for spectate",but then i also noticed i could "hit" those guys who i killed and were in the warm up. This was a little bit annoying, especially when they get in front of someone that we are trying to kill.

Probably the common question would be: How can you know you were hitting someone ?
When I shoot some spectator, blood particles appear followed by sound of bullets hitting someone

Besides that, if someone have done /spectate or clicked the emerald block, I can see what item are they holding(compass, emerald block, etc.)