TK does do strange things with its inventory. I was looking at a *A award flight (OZ miles) from LAX to IST for about a week, and there were 4 seats available every single time that I checked. On the day I decided to book, the J availability for that specific flight vanished, and I was forced to settle for Y on that segment. A few days later, all of the J seats reappeared. I had to pay a $30 change fee, but I was able to rebook in J.