From post #2 and #5, it seems that United will be thinking in terms of the fare difference between MAD - FRA - SFO and FRA - SFO. I can definitely believe that the price difference would be nil. Unfortunately, I was thinking I would be refunded somewhere in the range of a one-way (business class) ticket from MAD - FRA. I should have asked more questions on the phone with United. This could be an expensive mistake.