Wrong hit particles in Minecraft?
Solution 1:
Nope, that's totally correct.
What you're seeing is the damageIndicator particles. It is used when a mob is damaged by a strike (when you've timed your attack correctly, as opposed to spam-click post-1.10).
You may be confused because they are indeed very similar to the breeding particle, only darker (in terms of when using the default resource pack).
See http://minecraft.gamepedia.com/Particles for a list of particles in the game.