I've found Mindpearl in CPT (no experience with other Mindpearl offices) to be very easy to work with; however there does seem to be evidence that they interpret some rules differently than one might encounter elsewhere. Oneworld is not monolithic, and that's an understatement.

My recommendation is just to add (mentally) an extra US$125 to the price you're quoted, then have the ticket re-issued to your liking as soon as possible after your first flight, based on an itinerary completed and koshered with the AA RTW desk or its equivalent. Less stressful for all concerned, and the $125 is a cheap price to pay for getting it just the way you want it - choice of carriers or codeshares, extra segments, blah blah.