I called AA RTW yesterday to change the date on one flight segment of my current AONE5, and was told that the ticket would need to be reissued (but no fee) and to expect a confirmation email in a couple of hours.
Email had not arrived 24hours later, so I called again and was told that it was still queued for reissue, but she would do it immediately, and she gave me the new ticket number on the phone.
I questioned why a simple date change needed a reissue and she said that they had been having problems with the different airlines' computer systems not communicating properly, so now all date/time changes require a reissue and a new ticket number.

Probably makes it even more important now to make sure you get the email with the new ticket number, every time you make a change, and keep track of the most recent ticket number, in case of questions at check in (especially with other airlines.)

(This only applies to e-tickets, obviously.)
Happy Travels.