Join Date: Apr 2011
Location: Treasure Coast, FL
Programs: DL Diamond, Marriott LT Plat, HH Diamond, Avis Preferred Plus, National Executive
Posts: 4,628
No clue why it happened but for future reference you should get a $200 travel voucher and the fare difference for an involuntary downgrade.
I have the two times it has happened to me and think that is the standard compensation from DL.
Something to consider if it happens again.