A few weeks ago the BA check-in agent at LAX refused to take an AONE coupon that showed an AA flight and sent me to AA to have it "stickered". AA does not do stickers, so the AAgent had to re-issue the xONE ticket. Some kinda miracle that it all took place in time to get on the BA flight - one more aspect of why it's not so much fun anymore.

Aside from that, the reason I was using an AA coupon on a BA flight was that Cathay had canceled my AA LAX-LHR booking a week or two before (so claimed the AA atw desk). Another miracle that I happened to call in then to add a segment, else I would have been surprised to find no reservation when I came to board the AA flight.