In Wade-Giles a P is a B and a K is a J. So Peking should be pronounced Bejing. So there is no real problem here, except for years no one ever bothered to check out what the pronouncation should be. If I understand things correctly Wade-Giles has more sounds available to it and thus can give you a better flavour of Maderin. However for simple things like place names it makes very little difference.