Interesting but not unusual when 4-class plane operates on a 3-class route. This may be why I can't do OLCI on my YYZ-LHR 788 flight tonight (even though I did pre-select my seat) and got a message to report to airport early for a ticket reissue. Nor can I pull up the seating chart on EF. May be a 789 tonight? Though I also find on this flight I often receive a courtesy upgrade from WT to WT+ while in the lounge.

Though with the collapse of the Alberta oil industry, doubt BA would be able to sell any F seats so decided to scrap that cabin (in spite of what the booking site might offer...did you actually proceed to book that F seat to see if the engine would actually confirm it?). When F cabin is used as J, airlines generally offer those F seats to their elites.