Light reflected directly from an emitter is substantially diminished in strength

[JustinTimeCuber]

Relates to #608.
Scene file:
default_2022-12-09_15-35-06.zip

To test this, I set up a sea lantern behind a wall of black concrete (very low albedo block) with a narrow hole to allow a beam of light through at an angle. I disabled sunlight and skylight and set emitter intensity to 10000. I added a "mirror" of 4 iron blocks, which I set to have both specular and smoothness of 1.
Setup:

Result:

As you can see, there are four lit areas with the light paths as follows:

A - Sea lantern -> Ground -> Observer
B - Sea lantern -> Ground -> Mirror -> Observer
C - Sea lantern -> Mirror -> Ground -> Observer
D - Sea lantern -> Mirror -> Ground -> Mirror -> Observer

Because the mirror should not decrease brightness significantly, all four of these areas should at least be at comparable illumination levels. However, C and D are notably much dimmer.