If I had a nickel for every time I got a pricing error on UA's site....

The site does not like when you make changes to reservations that are pending. Here's some of the issues I've had:

-Taxes stripped out on the confirmation screen
-Pulling mileage upgrades from someone else's account before ticketing yields a price that says something like "$0.00 and 221 miles"
-Using cash from TravelBank sometimes yields the wrong price on screen

In all those cases, I've always been charged the right amount for the ticket on my credit card.