I think UA did the "stealing" here. I know this subject has come up before but what exactly does confirmed upgrade means in the eyes of UA. I quote this description of SWU from ual.com: "Experience our new first and business class cabins and arrive relaxed and refreshed—on many international flights, you can even stretch out in 180–degree lie–flat seats. Plus, if seats are available, these upgrades can be confirmed as early as the time you request them. Now that’s peace of mind." The OP had a confirmed upgrade into BC. If UA can take the upgrade away at any time, it's not confirmed in my books.