A quick question to add to this thread, as I'm encountering the same problem - in my case, leaving Africa (Tanzania) rather than traveling there. For weeks, United has been consistently listing phantom availability on a specific Turkish Airlines flight from JRO to IST. The flight is listed on multiple days, but it's a phantom on every date where it's listed (or at least every one of the 4 or 5 dates I've spot-checked).

Is it possible that space will open up on that flight, or should I simply give up and book another itinerary that's currently available?