This is really quite poor isn't it - and sure, while the customer is not committed to completing a purchase until the "second final" screen as noted above, that such a basic failure in process is tolerated really speaks volumes for the airline's ability and desire to get things right (and as an aside, as someone who works in a large, old business in another sector I know that fixing the ancient IT that modern consumer websites sit on is mind-bogglingly complex and expensive - but still)
BA is my main airline and I find more positives than negatives, but stuff like this really has me rolling my eyes