I have experienced similar things in the past week, all with the same AA agent, who is actually very nice, and I don't want to mention his/her name.

The first one was to date change a DONE4. It was a CX flight. I was told I would have to go to an agent to have the ticket reissued. I was in Sydney at the time, where there is no AA office, and didn't particularly want to go to a random travel agent and see what they could do, so I called CX office to see if they could see the booking, which they could. There was no problem at checkin.

Then a couple of days ago, I made changes to a separate DONE4, this one did not involve any CX flights, only AA and QF. They were only date and time changes, but again I have been told (coincidently, by the same ticket agent) that I will have to go an AA ticket counter to have the ticket reissued. I haven't done this, but flights are now tomorrow morning from LAX, so I should probably get to the airport a little early incase I have any problem. Will report back with the outcome....