Repro:
01 - Ensure Auto is enabled (Lighting Settings >)
02 - Create a Scene with a cube and a plane.
03 - Make these objects Static.
04 - Set the default directional light to be `mixed` mode.
05 - Wait for lighting precompute to complete.
06 - Disable Scene View lighting using the `sun` icon in the Editor UI.

Note:
Baked components of lighting are retained. In Mixed mode this creates an effect which is very hard to read as this is just indirect. This can be seen in the attached screenshot.

Expected:

The original purpose of this feature, if im not mistaken, was to enable the user to disable distracting / dark lighting so that they could more easily work in the Scene. It's supposed to enable a light locked to the camera as a "headlamp" which then enables easier visibility in such cases.

I'd argue that the current behaviour is undesirable. we should be able to see the Scene with no lighting _at all_. Im not sure of the benefit of disabling just the realtime lights when we retain their baked output.

Notes:
- Reproducible in 2019.2.0a11, 2018.3.12.f1, 2019.1.0f1, 2017.4.25f1.