I tried to book a ticket from Miami to Shanghai today and to apply a US$500 certificate United had sent me after the problems with my flight to Dublin over the summer.
Each time I tried to book the web site error-ed and told me to call Web Support. Having done this they told that it was a class of service error with my return. Humm!
I did notice the error above where the difference between £1443.40 and £311.65 is apparently £705.41 and not the £1131.75 I was taught in school.
There is a (small) prize for anyone who can work out how unitedairlines.co.uk got the price above!