[MENTION=118082]OskiBear[/MENTION] - agreed - we booked our tix on the Argentine website with a bit of help from Google Translate after finding the problems you noted with the US website.
While in Argentina we received a couple notices about our reservations so needed to visit their office in El Calafate and Mendoza and found both experiences very good.
I wouldn't hesitate to make future bookings using their website knowing a bit more about the process now and how to handle changes as they come up.