I used miles to upgrade an itinerary in January last month before the required number of miles was increased. 3 out of 4 segments were available, the 4th was waitlisted.

While I was out of town this week, I received a phone message from UA saying my 4th segment had cleared and to call UA reservations.
I called today and was told that I had not called back within the required time period and that my upgrade had been given away...Huh? I paid for the upgrade with miles, it was waitlisted, obviously I WANTED the upgrade I paid for. What was there to confirm?
Eventually, the res agent was able to get it back.
But this seems pretty flakey to me....