Used to be the case that when you redeemed a standard Y award the system did the "We have requested a complimentary upgrade for you" thing.

If you cleared prior to the gate, you did OLCI and know one was the wiser. But if you cleared at the gate, I have some fond memories of pleading with the gate agent to let the upgrade stand since it was a glitch in UA's system rather than my fault (and my nice E+ seat had been given away by the upgrade).