Filename of glow map is assumed, rather than read from shader
When a texture, such as for a light, has a glow map defined in it's q3map2 compliant shader, darkplaces ignores this. You can even comment that section out entirely.
Instead DP tries to load a file of the same name as the shader, but with "_glow" inserted before the dot and extension. If it finds this, it will apply it with blendfunc add, ignoring any blendfunc specified in the shader. This also happens for filenames with "_luma" before the extension.