I went to buy a PHX-MSP-YUL-JFK-ATL-PHX ticket today. The fare came up as $279.45. After the screen where I entered emergency contact information I got a message saying "There has been a fare change. Your original price was $279.45. Your new price is $279.45. Click continue below to confirm the change". I did and it reverted me back to the "Click to Purchase" screen.

After three times doing this, I started getting booted back to the Purchase Tickets screen with an error message saying "I'm sorry, this fare is no longer available, please try again". When I would, it would again show me $279.45 but wouldn't let me buy it.

Eventually I bought the otubound on NWA.com and the inbound on Delta.com. Shame as it cost me an extra $15 in taxes and fees.