How to reproduce:
1. Open the attached "UnityDeferredParticles.zip" project
2. Load "SampleScene" scene (found in "Scenes" folder)
3. Enter the Play mode

Expected result: quad with "Particles/Standard Surface" shader does not reveal GameObjects behind it
Actual result: quad with "Particles/Standard Surface" shader reveals GameObjects behind it

Reproduced with: 2017.4.33f1, 2018.4.12f1, 2019.2.10f1, 2019.3.0b8, 2020.1.0a9

Notes:
- reproduced with "Cutout", "Additive" and "Modulate" Rendering Modes for "IssueParticleShader" ("Particles/Standard Surface" shader)
- "Standard" shader with "Cutout" Rendering Mode does not have this issue ("Additive" and "Modulate" Rendering Modes not available)
- the issue is not visible in Isometric mode
- one workaround would be to set Rendering Mode to either "Opaque" or "Fade" or "Transparent" for "IssueParticleShader"
- another workaround would be to set Rendering Mode to any other than "Cutout" for "BG", that is used for the GameObjects that are behind the quad with "IssueParticleShader"