I have seen this a few times. I actually have a few bookings like this that don't show up anymore to purchase BUT still show as booked by me. A couple of MCI - MCO (connecting thru BNA). along with MCO - MCI (connecting via RDU). Also had a MCI - SNA (connecting thru DEN) as well. What happened as far as I can tell.. there system released a whole bunch of flight choices but then they decided to pair the list down and remove some. The individual flights still exist and your booking is still intact. You just can't re-fare it out.