Steps to reproduce:
1. Open the attached project "Case_1160531"
2. Navigate to Project -> Assets -> Scenes and open "SampleScene"
3. In the Hierarchy select "GameObject"
4. Press F to focus it in the Scene
5. Make sure that "Show Bounds" is checked
--Notice that Particle Systems bound size

Expected Results: Particle System Renderer with Negative Speed Scale values creates the same Particle System Bound as Positive values would
Actual Results: Particle System Renderer with Negative Speed Scale values creates smaller Particle System bounds

Reproducible with: 2017.4.0f1, 2017.4.25f1, 2018.4.2f1, 2019.1.5f1, 2019.2.0b5, 2019.3.0a4

Notes: This bug is not consistent and works differently with every Particle system but usually setting Speed Scale to -1.2 and Start Lifetime to 1 reproduce the bug. Turning off Rendering and Turning it on Fixes the issue.