This was not the cas before, but I just looked at some other random routes (like CDG-BOS, CDG-SLC, CDG-JFK) and you are correct : on AF site, all DL-operated flights are sold only under DL code, while all itineraries involving one connection has the DL-operated leg sold under AF code. I really don't understand why because there is no regulatory restriction AFAIK. I could eventually understand if it was not available on the website/app but the fact that even the booking centers cannot see it in their system goes beyond any logic if a simple OTA like Expedia can sell it to you. The fact that AFKL teams cannot sell AFKL-coded tickets and prefer to let the sale to some OTAs is a strange business decision.