oneworld - online tool and the ticketing airline

What factors control the ticketing airline when using the online tool? I want to be sure that AA does the ticketing in my case but I need to start in South America.

What factors control the ticketing airline when using the online tool? I want to be sure that AA does the ticketing in my case but I need to start in South America.

From oneworld.com:
Question:

Who is my ticketing airline?
Answer:

The ticketing airline is indicated on your confirmation page. In most cases, it will be the airline whose code is on the first flight of your itinerary.

AA=American Airlines, AY=Finnair, BA=British Airways, CX=Cathay Pacific Airways, I6=MexicanaLink (ticketed by Mexicana), IB=Iberia, JC=JAL Express (ticketed by American Airlines), JL=JAL (ticketed by American Airlines), JO=JALways (ticketed by American Airlines), LA=LAN, LP=LanPeru (ticketed by LAN), KA=Dragonair (ticketed by Cathay Pacific or Dragonair), MA=Malév, MX=Mexicana, NU=Japan Transocean Air (ticketed by American Airlines), QA=MexicanaClick (ticketed by Mexicana), QF=Qantas Airways, RJ=Royal Jordanian (ticketed by American Airlines), XL=LanEcuador (ticketed by LAN), 4M=LanArgentina (ticketed by LAN), S7=S7 Airlines (ticketed by American Airlines).

Fly AA on your first segment. You should end up with AA also if you book your first segment on another carrier but as an AA codeshare. There are a few exceptions, of course, such as AA always ticketing for RJ.

In general, the ticketing carrier will be the carrier whose code is used for the first flight. There are some exceptions (S7, JL and RJ are ticketed by AA).

eg, PER-SIN, QF77/BA7377. Using the QF code will cause QF to ticket, using the BA code will have BA ticket.
SIN-HND, JL36/QF4025. Using the JL code sends it to AA, using the QF code sends to QF.

However there has been a bug in the tool for some time (not sure if fixed yet) which will cause the booking to fail on the last screen of the process when AA issues, but isn't the operating carrier of the first flight.

Thanks for great answers!

Last month, July 2012, I tried to book DONE4 originating from DXB bia online tool.
1st segment is DXB-LHR.
I chose AA code share. After price was quoted (AA head and magically in USD), and I entered credit card information, system can not handle process.

I change 1st segment from AA to BA (same flight).
Price was quoted in AED. As you know, BA as a head carrier, I need to contact the local BA ticketing office to finalize process.
So, I call BA office in UAE.
Unfortunately, they refused to accept credit card payment via phone.
They provided me phone number of Jpaan local office.
I called BA Japan local office. They can issue ticket, but ex-Japan price.
Furthermore, BA agent said they set an upper limit of credit card transaction via phone. So, I can not make ticketing via phone.

To the end, I contacted CX Japan office.
They has no credit card limit via phone.
Magically, they issued the ticket that was originally booked by OW online booking tool. That means my booking record locator is same 6 letters provided by OW online tool.

However there has been a bug in the tool for some time (not sure if fixed yet) which will cause the booking to fail on the last screen of the process when AA issues, but isn't the operating carrier of the first flight.

I didn't know THAT was the source of the bug; i.e., AA as issuer but not operating carrier. I would like to be able to ticket my RTW's ex-AMM with online tool, but have never been able to do that as of yet.