This is not a mistake fare. It just like Lan.com glitch, which drops YQ fuel surcharge at the time of ticketing. this system glitch has been around for almost a year now, but it's for Europe Cities. Now it's working for China too, don't know when UA will fix this.
The deal is working from manys cities such as SEA, CVG, DTW, NYC and many more, you just have to search on ur own and follow the step below, ticket to Beijing is higher than ticket to Shanghai, the cheapest ticket to Shanghai so far is around $678 with return less than 30 days from departure NOTE: The deal may not work from SFO, but it does work from San Jose.
Also, your departure date must be later than Olympic time in order to get cheaper ticket.
The change fee is $250+ fare difference, however, I do not know whether the YQ charge will be added back if you change ur ticket.
1 go to united.com
2 select multi city
3 Flight number 1, xxx(your departure city)-PVG/PEK
4 flight number 2, Pvg/pek-xxx
5 Flight number 3 SEA-YVR, Select a date after your Flight number 2 date. Adding this segment will result system drop YQ fuel surcharge.
6 Select search by Price.
7 you will see the price and proceed to booking like any other
after u finish your round trip, you throw that SEA-YVR leg away.
Thanks to Flyertalk bring this up.