To reproduce:

1. Download attached project "Mini-Momentum.zip" and open in Unity
2. Open "Particle Collision Debugger" scene
3. Enter Play mode
4. In Hierarchy select "Weapon" game object
5. In Inspector window, on "Weapon" script press Fire button with left mouse button

Expected Result: In Console observe that it prints this log message:

Collision Events 1/1
UnityEngine.Debug:LogFormat(String, Object[])
Weapon:OnParticleCollision(GameObject) (at Assets/Scripts/Weapon/Weapon.cs:26)

as many times as the Fire button was pressed.
Actual Result: In Console observe that it prints log message many times - from 1 to 14 and more

Reproduced on Unity 5.5.4p1 and 5.6.2p2
Could not check for regression on Unity 2017.1 and 2017.2 because particle system becomes broken

Note: This issue appears on both Windows and OSX

Forum post: https://forum.unity3d.com/threads/particle-system-sub-emitters-colliding.481404