This is really not a surprise. With the exception of the few flights discussed on here, DL has not had domestic Business for years.

And, DL really hasn't had international first for 7 years now, so their configuration model has been pretty clear for the last 5-7 years

But, DL should put you in domestic F when travelling on an International C class (award) ticket. I believe their rule is domestic Y, then International C, but in my past experience they have always put me in domestic F after I (politely) disagreed my way up the food chain. But that was always early in the game when availabilty was high....

Try calling them and see what they say...