Steps to repro:

1. Open attached project and 'SimpleReflectionprobeTest1' scene;
2. In the Lighting window click 'Generate Lighting' button;
3. Observe the intensity of the baked reflection.

Expected result:
The reflection's intensity is the same as the scene's light intensity.

Actual result:
The reflection's intensity is lower than the actual scene's intensity. See attached video.
Regression introduced in 2018.1.0.

4. Select 'Reflection Probe' gameobject in the Hierarchy;
5. In the Inspector click Bake button;
6. Observe that the reflection intensity is the same as the scene's one. See attached video.

Notes:
- Reproducible in 2018.3.0a8, 2018.2.2f1, 2018.1.9f1, 2017.4.9f1;
- Reproducible on Windows and OSX;
- After baking probes from the Probe's Inspector or from the Bake Reflection Probes option in the Lighting window for the second time, the lighting in the reflection is consistent with the scene's light intensity.