When translating a translated TEXTURES lump, ZDoom does so correctly and remaps the corresponding values.
However, GZDoom does not. GZDoom, instead, leaves the previous translation in place.
What I've done here, with test.pk3, is created a TEXTURES lump that makes the player sprite blue, using a direct palette remap.
Then with DECORATE, I created a TestActor that takes the exact translation and puts it back the way it was originally. This is the point where GZDoom and ZDoom differ - GZDoom (in GL) doesn't handle the translation the way ZDoom does.
As for the "shit you didn't want to wade through", Torr mostly wanted to know your actual stance on this more than anything. It's an issue for Skulltag because this method is used for one of the flags in a mod you'll obviously never care about or play.
Spoiler: Thar be screenshots here!And here's a test wad...
