How to reproduce:
1. Open the attached project "case_1146514-ParticleEffectPanelCameraRotate" and scene "SampleScene"
2. Select "ParticleSystem" in the Hierarchy to make the Particle Effect panel appear in the Scene View
3. Right-click to the left of the Particle Effect panel and drag (click inside the region below the panel's top bound and right of center of the Scene View window)

Expected result: Scene View camera rotates according to mouse drag direction
Actual result: Scene View camera orientation does not change

Reproducible with: 2019.2.0a10, 2019.2.0a12
Not reproducible with: 2017.4.26f1, 2018.3.13f1, 2019.1.0f2, 2019.2.0a9

Note: other actions such as box select, pan, zoom, interaction with transform manipulators also don't work when initiated from the described Scene View region