I'm not sure if it's Oneworld madness, or ITA madness...!

If you were able to book it this way, I'd be nervous about both OLCI and seat selection for many of the flights. I'd especially be nervous about the AMS - PHL flight with the BA flight number ---- each time I've had one of these (BA flight number on a TATL codeshare), both online and and Kiosk check-in were not possible. YMMV