Today, I tried to book a IAH-MEX-PVR RT using the Delta website (codeshare on AeroMexico). Delta website worked well, and quoted me a wonderfully decently priced rate of 488 USD RT over New Years Weekend. Went through the entire booking process, picked out seats, then tried to pay for the ticket. At which point the Delta.com website says...."Oops the fare is now 1100 USD higher. Do you wish to proceed?" Of course not. I'm flying UA/Aeromar.

Is it normal for Delta to not have reliable pricing on their website?