How to reproduce (or just watch attached gif):
1. Open my attached project "test1".
2. Open scene particlesys.unity.
3. Play the scene
- Note how every time a particle collides with the sphere, the sphere changes colour and the connecting particle disappears
4. Move the sphere elsewhere in the scene view
- Note how the sphere still changes colours sometimes and some of the particles disappear

Reproduced with: 5.4.0p1,5.4.0f3, 5.3.5f1, 5.3.4f1, 5.3.2f1, 5.2.0f3.