Just went to book YEG-IST, and was offered $2700 per person (2 of us travelling together) for a Flex fare. Worked out that we could fly YEG-ZRH for $1500 each and then ZRH-IST on TK for $700 for two. Much better deal. So I booked the TK flights and then backtracked to AC to get the initial outbound flight. Just as I was completing the transaction, I got an an error message that said there was an issue with the fare and I should call. I called and was talked through the booking again. Now the YEG-ZRH bit was showing up as $1900 each. How lovely. Still cheaper than the AC itinerary to IST, but $400 more than 15 minutes earlier. It seems that in some other timezone (EDT) the clock ticked past midnight and the fares got changed. Then of course, I had to put in my personal information because we would be flying through the US. That's the part of the US that's between YEG and ZRH. Guam, I suppose. Bottom line: don't book near midnight Eastern time or you can get burned for a few hundred bucks.