Okay,
Maybe this is voodoo territory, but polystyrene caps are "polarity sensitive" as Martin says in the build documents, but only to the extent that it's slightly better shielding for the cap to have the foil side connected to ground (unless they're used where one side isn't connected to ground in which case it doesn't matter) Correct?
Well, numerous of these styrenes are used where connected to ground in this circuit.
Does anyone know how to determine the foil side of a polystyrene cap? I can't for the life of me see it with my eye. (I happened to order the Xicon polystyrene caps from Mouser but they came as radials not axials.) Oh well. I don't really care about that, just how to see or determine the foil side of the cap.