How to reproduce:
1. Open a project with HDRP template
2. In the Scene window disable scene lighting (lightbulb button on top of scene view)
3. Observe the Game window

Expected result: Game window does not change
Actual result: Game window turns black

Reproducible with: 2019.2.0b1 (6.7.1), 2019.2.2f1 (6.9.0, 6.9.1), 2019.3.0b1, 2020.1.0a1 (7.0.1)
Not reproducible with: 2018.4.7f1 (4.1.0, 4.10.0), 2019.2.0b1 (6.5.3)

Note: sometimes the Game window does not update (turn black) until the mouse is dragged on it