On my itinerary saved in the planner BA is the first carrier (JNB-CPT) so it's interesting that their new price isn't being reflected.
I would indeed ticket it if I could CPT-DOH as the first flight as I want it to be (and pay in USD which I think is impossible (ZAR funds aren't available to me at the moment but USD are)). If I ticket it as is it won't help me when I come to change it, as it'll re-price entirely given I'd be changing the first sector.