I experienced this last week using ba.com. I was trying to put an itn together with gru to mvd and then mvd to gru to jfk,, all on tam. For several hours while i was putting things together with the missus, the flights were showing lots of seats and multiple options. When i went to book, poof everything gone for months on end. Called the exp desk and she said nothing is coming up for months. I waited a few hours and then everything came back and i called back and booked it. This was the middle of the night brazil time, so i figured it was a system update.
In the end I got two seats in y gru to mvd and three seats in j mvd to gru to jfk using aa miles. These are for flights leaving first week of feb 2015. I tried to book the gru to mvd with avios to save points but the website kept erroring out at the ticketing stage (after the cc payment, passenger info,etc.) so i figured i had better grab the y seats while I could with aa miles. Revenue for that route was $600 a piece in y one way, $350 rt