This happened to me tonight. On FLT 460 SNA-SFO-YVR. Saw last night that I was not on the list for the SFO-YVR leg. Didn't clear UG SNA-SFO, but now I'm in 12D and there is an extra seat in F. FA says gate agent chooses who gets it. Gate agent says SHARES wont let her assign it to me so I can't have it. GS representative was working in the UA Lounge at SFO and confirmed this, and said there was no way to fix it.

I called the elite desk and in the limited English that the rep spoke, she informed me that my flight was from SNA-YVR and that it did not stop at SFO - which was quite amusing but not very helpful.