Long story short: booked on Friday for SFO-IAD-RDU. Wanted to upgrade with miles, but the first segment was WL only. No problem. I called to WL for that leg:

Agent: "Sorry, you cannot apply for UG on only one segment, has to be both."
Me: "Whatever, fine, go ahead." Agent confirms UG for IAD-RDU and WL for SFO-IAD. I check My Itin... WL is also for wrong class (NF instead of NC).

Call again:

Different agent: "Sorry, you cannot apply for UG on only one segment, has to be both. I see you are WL on first seg and CF'd on second."

Call again:

Different agent: "Of course you can apply for only one segment, sorry for your troubles. And, yes, let's get that class of service corrected." Agent processes UG request correctly, removes CF'd UG for IAD-RDU. WL looks good on My Itin.

Check it later that day, just to make sure! Shonuff, back to confirmed UG for the 45 min IAD-RDU flight. AAARGH!

At this point I was tired of dealing with it, and also didn't want to risk having someone go into the PNR to fix it, only to somehow remove and re-list me for first leg WL, thereby 'losing my place' on the UG list (first on / first off!).

I obviously don't want to use miles for IAD-RDU, so without having someone messing with the itinerary now, when is the last possible moment I can cancel my CF'd UG for that segment and have the miles redeposited?

Thanks in advance for your help.