Sounds like an IT bug to me as well. I was searching for some domestic flights for 2016 several weeks ago, and on one week, availability was what you'd expect -- plenty of discounted fare classes still available. But for the same flights a week later, the only buckets with availability were full-fare first or Y/B (which seemed unlikely for these flights so far out). A week or two later, I checked, and discounted economy and first were available.