It's casting a shadow when it shouldn't.
So I checked and the model casts a circular shadow when lit from below, which definitely isn't ideal, but most of our early light models cast unattractive shadows by default. That's why mappers typically set them to noshadows manually or use the entities that do it automatically. If that wasn't done in this case, isn't it a map problem rather than a model problem?
If so, a barely visible hot coal texture inside the cage lamp goes black on custom skinned models?
Collateral damage seems to be minimized there.
Except that that black texture would also cast shadows, so you would potentially be making the problem worse, not better.
There are at least ten models that use that texture, all of which have been around since the early days, so the odds of someone having done something custom with one of them seems high.