Concierge at YVR told me so. This may be a bit different because it was YVR - SYD (same flight number), but he told me an E35 (this was a year ago) boarding in Toronto with a Tango Plus and who upgrades from YYZ to YVR, and gets wait listed for YVR-SYD, TRUMPS SE ON LATITUDE, going from YVR to SYD!!!!!!!!!!!!!! He told me it was outrageous and that I should write in to complain. Again though, the same flight #, might have something to do with it.

Additional evidence, though not of a very compelling nature, is a non-status PAX I upgraded last year YYC-YVR-SYD, who got upgraded at the gate on YVR-SYD, though that might has just been a fluke; and the fact that in the past two years, I've only missed one upgrade YYZ - PHX, and upgraded dozens of others as a connecting PAX.