The various Oneworld systems are incompatible and they really cannot see your PNR info unless it is explicitly pushed from one computer system to another. Certain transactions cause an attempt at an automatic push (usually this results in each system having a different subset of the info). When an agent runs into this on a reissue you will have tremendous problems unless they are very skilled and persistent (usually they must over-ride several different things in ways that are not usual). Be glad you didn't try to reissue with BA who would have charged a 25 GBP fee on top of the 75 USD reissue charge (and made sure you got many hours of "entertainment" for that 25 pounds).
With the move to e-ticketing across OW airlines I am curious to see how these kind of problems are resolved; I'm holding an e-ticket with flights on CX, AA, BA and have had no problems so far, but imagine when the agent says: "I'm sorry sir, there is no reservation in our computer for you". And there is no paper to prove otherwise (the PNR printout is easily forged so they can't possibly accept that as proof).