"$basemapluminancephongmask" not working

[Odium]

Can anybody that has experience with phongs/VTFEdit explain to me why $basemapluminancephongmask doesn't work in Garry's Mod? Whenever it's applied to a material, it becomes extremely bright (unlike SFM where it works properly) and I'd like to know if it's possible to get it to work for GMod or if it's broken forever.