Yes, this is the only time it's ever happened to me. I've flown their biz class 3 times (agree that the chair/bed is very comfortable and i also like their food infinitely better than AirFrance's). It happened on my outgoing segment from AMS to BOM but on the way back i got the credit. The agent explained to me that the way back was a "Delta marketed fare" and did NOT qualify.
ATL