I don't know for sure, but it sounds like there are a decent number of reports of this happening and they are all around reservations that are being walked. There is a possibility that the DVC systems are being set up to monitor reservations being walked and start to block dates temporarily to prevent walking.
Obviously, in order for that to happen they would have to do some coding and it would be a consistent behavior. So they could do it for all reservations or possibly just high demand rooms (GV's, Concierge, etc) and prevent members from walking a reservation indefinitely.
But, outside of that, no one knows how the DVC systems work and there are 100 possible scenarios or situations where the room is not available. Maybe the room was taken out for maintenance and then later released for some VP to book. Technically, not against the rules, but definitely not "fair", although walking reservations could be seen as unfair too. Also, I think we have all seen where all availability is not immediately available at 11 months, as others have eluded to as well. I have seen where availability seems to be added several days or weeks after the 11 month window, especially for high demand dates. Rooms may be rotated through maintenance cycle days throughout the year automatically and then released later when it is determined it is needed or not (or maybe they get an inspection day periodically).
But, the truth is that no one knows and members don't have the right to know who has a reservation in front of them. As members, we have a right to book at 11 months if a room is available, I don't think we have a right to know why there is not availability, even if it is suspect. Outside of actually filing some type of lawsuit and going after Disney to disclose how the systems work and why this might occur, I doubt we will ever know. And, even if that were to happen, we would then only know this one scenario and again their might be 100 more that we don't know why.