That's always been the theory as I understand it, too... but getting that to happen in practice is almost unheard of in my experience. I've literally had times when I've been dealing with even a single ticket including both AA and BA flights, booked on AA stock but with BA fares, and had both airlines insist the other airline had to take care of anything that went wrong (or I even just wanted to change within the existing fully-flexible fare rules), either because "it's an AA ticket, and BA can't do anything with it" or "it's a BA fare, and AA can't see the rules" And I did ask, yeah, but doesn't oneworld mean either of you should be able to handle it?

If BAcrewmember's handle is what it sounds like, I have also noticed that there seems to be a very different perception of what the alliance is from flight crew to ground crew to ticket desk staff to telephone staff. The former saying something like the post above, and the latter looking at me (or speaking to me) as though I had asked for a free flight because the sky is blue and so are my mom's eyes.