I saw the same thing on my booked flights from DFW to MCO. First, the flight I have always taken out, suddenly got full, unless I wanted to ad another $400 to my bill. We had decided to just go ahead and leave the night before, so I booked, and yep, my flight was available again. I am still happy to be leaving a day early. I am sure it has to do with Delta pulling out of DFW yesterday. I am sure many people will be scrambling to book a flight now. Glad we have ours!
Have a great trip shatzjsl!