It's the same in economy, though I'm not sure on who's side the problem is. Is it EI jacking up BA codeshare prices or the other way around. Just did one this weekend return, 100 cheaper to book 2 flights individually than as one through codeshare. BA out of Cork is very hefty for shorthaul, though longhaul is more reasonable.
Take a closer look at the booking class! For some reason, if you try and book shorthaul flights on the BA site, from ORK, even if you select economy, it quotes Club Europe fares! I called BA about this before, and was told that that was the best available fare! When I mentioned that if I book the flights individually it's a fraction of the price, and BA economy seats are available... So I think BA just don;t want Economy passengers for shorthaul, orginating in ORK! They only want the premium PAX!