The agent obviously didn't know what she was doing - she should also have contacted the OneWorld RTW desk instead of International Desk Tariffs. A date change is acceptable and should have been just corrected by a pen.

I think post 9-11, airlines are just cautious of changes that do not reflect what it says on the tickets.

Word of wise - next time, travel on open tickets, and get a print out of your latest travel itinerary to show to check-in agent.