Interesting story--and that flight from SIN-IST is overnight, is it not? (which really makes the downgrade to Y all the more intolerable).
Reading some trip reports I have found more than the normal number of concerns re customer service from TK...hard product seems fine, but....
While playing around with our next award tickets, I was looking (like many do) at TK to transit through IST en route to Hong Kong. Glad I ended up picking LX and TG.