After a lot of time on hold and escalation to a supervisor I've been able to confirm that the website is selling tickets claimed to be eligible for an immediate upgrade but that aren't.

Having confirmed there was space in U class for PDX-LAX, SNA-PDX when searching the website with the upgrade preference set to "Platinum" the site quotes $447 round trip. But clicking button to put the itinerary in the basket the outbound shows up in O class, which isn't eligible for an upgrade.

Seems like this might not be an isolated problem. I ran into this trying to change the dates on an existing reservation over the phone and the supervisor said there was an add collect when there should have been a small refund based on the price the website was showing. That's when she noticed the class of service was wrong.

So just a heads up when booking a ticket you be sure to confirm the class service is correct or the system isn't going move you to first class.