@breakin @lisyarus I spotted the same issue in my own code ( https://avoyd.com/ ) yesterday when I added support for emissive factors > 1.0 in my non-texture based export pipeline for .obj. Many thanks for submitting an issue (you beat me to it)!
As you found, using a texture map for emission fixes this, and that's the main approach I use to export material parameters, but it's harder to edit so I still keep this option available.