ratypus, I cant comment on the IB part, but for BA I had the same issue, only shown the F cabin for seat selection, automatically assigned seats in the CW cabin, but cant see the CW cabin.
I called BA and they said they couldn't help with seat assignment as they had system issues. As for F, they said that would only open up if the CW cabin is full.
As advised in another thread, go to Quantas.com, put in your PNR and you can select seats in the CW cabin. You cant on BA but you can on Qantas - bizarre!
Enjoy Madrid! Not sure when you will be here, but keep mind that July and August can be hot, with temps sometimes exceeding 40C in August.