That subject has been heavily debated. And DL allows the confusion to reign because they can fall back on "it's really a coach fare but upgraded" if they have an IROP situation where there are more people with F tickets than seats.

My position is, on the welcome screen, there is an ad for Business Elite sale fares to Europe. I click on over, select First/Business, do NOT check the upgrade box, and I get a selection of fares, some of which are in F and BE. I complete the purchase (read the fine print too) and I have a confirmation of a First/Business Elite trip.

They advertized First/Business Elite. I purchased First/Business Elite. Now, here comes the fun part. My first flight is cancelled and there is no F space on the next one and they try to give me a coach seat. I say no, I paid for F, they say no, you paid for coach and got upgraded. Maybe 3 out of 10 people will buy this and take the coach seat.

If there's no space, there's no space. If there are 10 people from the cancelled flight vying for 5 avalable F seats on the next one, then there is a certain pecking order that has to come into play.

(IMHO) First to be bumped back should be non-revs, then SWUs who knowingly bought a coach ticket and got a "complimentary" upgrade, followed by PMUs. After that, they can do the fare shuffle and that's fine with me. Full fare F trumps my A fare and I'll either wait it out or do the walk of shame.