I hadn't, but I just did. Same behavior - the SEA-IST segment specifically doesn't show, but the TK intra-europe and now intra-Turkey segments do. The space is still there via EF, Aeroplan, United, and shows as saver space in TK's program (and I'm fresh out of Citi points). Damn, I'd really like to book this, too - 63k vs 90k Aeroplan.