Reproduction steps:
1. Open attached project (ReproProject.zip)
2. Open the "scene" scene
3. Click on the "Particle System" gameObject
4. Notice that some particles are not facing the camera (they look flattened, check Repro.gif)

Actual result: Some particles are not facing the camera.

Expected result: Every particle should face the camera.

Reproduced on: 5.0.4f1, 5.1.4p1, 5.2.4p1, 5.3.1f1, 5.3.1p1, 5.4.0b1