How to reproduce:
1. Open the attached project "case_1139865-ParticleFocus" and scene "SampleScene" (https://oc.unity3d.com/index.php/s/iLsYvUAQ9WMZNIS)
2. Select "ParentParticleSystem (no particles)" from the Hierarchy
3. Make sure that "Show Bounds" is enabled in the "Particle Effect" overlay window
4. Hover the Scene View and press "f" to focus on the selected system
5. Enable and disable "Emission" (or any other field) for the selected Particle System
6. Perform step 4 again
7. Select "EmptyParent" -> "ChildParticleSystem (flames)" from the Hierarchy
8. Repeat steps 2 and 4

Expected result: step 4 makes the Scene View camera focus tightly on all the yellow bounding boxes of the child Particle Systems and steps 6 and 8 do the same
Actual result: step 4 make the camera be zoomed out more than necessary to accommodate the selected systems invisible bounds and steps 5 temporarily fixes the issue until step 7 is performed

Reproducible with: 2017.4.24f1, 2018.3.11f1, 2019.1.0b9, 2019.2.0a10

Note: if you were to use "ParticleSystem (no particles)" in step 2 instead of "ParentParticleSystem (no particles)" the Scene View camera would end up at the particle system's exact location on step 6 which is different behavior than focusing on the "EmptyGameObject" where the camera stays some fixed distance from the Transform