I've experienced this issue on some simple domestic roundtrips this year. I will try to hold or purchase a $250 ticket and get a price change saying the new price is $300. I press hold/purchase to continue with the $300 price and get another message saying the price is now $250. It will go back and forth endlessly. I've cleared the browser session, started fresh and still have the same issue. Solution has been Web Services who always managed to ticket the lower price.