My guess is it's a combo. I'd heard via a property friend that Marriott was tinkering w/ the software during the time frame the OP was making his reservation & properties couldn't see reservations or mobile app requests from 10pm-2am Eastern time Sat night - which is just what you want to have happen when you're a property, right? (not) Also, as someone noted up thread, the property might have been sold out except for the one room that checked out late/early & since housekeeping was long gone, wasn't going to sell it at the property level & figured the odds of someone coming in late on a Sat night was slim so didn't close inventory (which would have meant MARSHA couldn't sell the room).. I think the OP is due some points, but obviously not for the entire amount since he did actually stay in the room.
Cheers.