I think the issue is the guidelines they are following.
I had no trouble deciphering the rules for using a voucher for TATL travel (only the overwater flight needs to have an AA flight number), but the first 7 or 8 AA people who read their documentation interpreted it incorrectly. That is a big fail in my view. The passenger should not know the correct interpretation better than the people the general public relies on to handle ticketing using these vouchers. I wonder how many passengers these employees denied the ability to use these vouchers for travel, or forced to pay higher fares by flying AA codeshares after getting to Europe, when all they could have used the OneWorld carrier's fare.

The OP's issue, thought minor in dollars, is substantial in showing an clear problem with AA. What are we supposed to do when stuck mid trip due to IRROPS due to AA issues? I have ample funds if AA doesn't pay the cost of being stuck, but that should not be the issue. It is AA's responsibility to cover extra hotel, food, and transport to that hotel if they have a mechanical issue causing an overnight delay. This is not a grey area. My last IRROP causing an overnight delay was with BA from Europe. I don't know what BA would have done if I had chosen a different place to stay. After the delay from TLV-LHR, I just wanted to rest rather than wait in a line trying to get BA to give me a hotel. Yotel is relatively inexpensive and somewhat convenient (landside in T4), and BA had no issues with that price , nor paying the additional 600 Euro compensation. What BA balked at was paying 5 euros for the sandwich I had, because I could not find the receipt and paid cash. Yes, it did make me think about ways to avoid BA in the future, if possible. Unfortunately, with my trip to Russia in a few days, they were in the OW itinerary that cost the least. The only other cost competitor from LAX to OVB was Aeroflot.................'nuf said.