Had a weird one on Friday. Was doing IAD-MCO-IAD (same plane, out and back--long story, but moved back my SGU trip to January but still wanted to get enough PQDs to put me past 1K now so I can start using GPUs for winter/spring travel).
Failed to clear on the outbound; finished
#1 on the list. I suspect buy-ups; simply wasn't worth it to me. Never showed up on the return waitlist (which was about 25-30 deep at the time, with 4 seats available), and my BP didn't say "added to upgrade standby list," either. GA wasn't sure but said "check in Orlando."
I ended up waiting until after takeoff on IAD-MCO, went online and forced an undo-check-in (by bringing up the "Change Flights" page and picking the "other dates" option). Checked in again, and voila, 2nd on the waitlist, pretty much as expected for a 1K on an L fare checking in ~2 hours before departure. They cleared 3 of us. Still not sure if I really was "on the list" and would have been cleared or not; I've certainly had it happen where I didn't appear on the list at all but still cleared a CPU. But I suspect if I'd waited to talk to the GA in MCO, I might not have made it...