Question About Chocobo Whistle And Mapitoto

According to the BGwiki page on mounts, when you update your chocobo whistle you have to trade it back to Mapitoto to update your non-whistle chocobo mount as well.

When I do this nothing happens. Is there supposed to be some kind of prompt or dialog? Does it actually update? Do you even need to actually retrade it to her or does it just automatically link up to your whistle?