My wife and I returned from our European vacation yesterday, flying back to the States AMS-LGW on BA and LGW-DFW and DFW-IAH on AA. Our reservations were purchased and ticketed on AA.com, all under a single PNR. On the outbound trip (to Europe), AA was able to issue us boarding passes for all oneWorld flights at check-in including the BA-operated LGW-AMS flight. However, on the return, BA's agent at AMS claimed that she could not print out our boarding passes for our LGW-DFW and DFW-IAH flights.

Why not? If this is an alliance, shouldn't alliance flyers be able to secure their boarding passes for all connecting alliance member-operated flights at their first departure airport?