Emissive material overblown with a specific lightmap parameters

I tried baking a super simple scene and for some reason it took me a pretty long time (bake times in the screenshot).
Another issue that I noticed is related to emissive materials. I created a green sphere, and set emission to 1. For some reason, that green sphere has no effect in "VeryLow" settings, has an overblown effect in "Low" settings, and looks normal in "High" and "Default".

Check out the screenshots under the spoiler, and note the greenish tint in the LowResolution screenshot.

Spoiler: Screenshot

I also created a custom Ligthmap Parameters object, set it's values equal to those of LowResolution and got that overblown emission effect. I then changed the "Resolution" property in the Lightmap parameters from 0.5 to 0.4, baked, and the emission looked fine. I changed it to 0.6, baked and the emission looked fine. I changed it back to 0.5, baked it and got the overblown emission effect. Why is it happening?