While not a SWA issue, I have had this problem with Thai Airlines. My brother in Thailand bought me a ticket for domestic Thai travel through his Thai travel agent. I wanted to make a schedule change at the airport and ended up buying a new ticket since the agency was not open on Sunday and their card was used. I did get a refund on the unused ticket later.

All in all, I think this insanity is limited to Thai Air. They don't create an issue if you fly on the ticket as originally made but changes that involve a fare change seem to be a problem if you didn't buy the ticket on a card in your name.