QuakeForge detail brush support was never actually tested. Otherwise how in the hell did this get through?
for (f = brush_faces; f; f = f->next);
f->detail = 1;
... AND ...
The QuakeForge tools use a different .prt file format.
So in other words they can't be trusted for this purpose and even if they could be they're useless anyway. Not portable to other QBSP tools and/or not usable by other Vis tools, you see.
Anyone with tools experience willing to chip in?