I am still relatively new to the whole PremEx "experience" (and as an aside I don't think it's going too well based on the last few weeks). Having been an AA PLAT for a number of years I thought the upgrade system on UA would be pretty similar. Now I don't know whether I am disillusioned by UA or just had a really bad experience with one particular check-in agent.

I was on the late flight from DEN -> LGA the other day and requested an upgrade at check-in as nothing had cleared in advance. The agent checked me in and I toddled off to the gate. On the way I noticed that I didn't have a seat assignment (although my reservation clearly had one) but rather a row of stars where the seat should be. On arrival at the gate I ask and am told that while I am waiting for an upgrade I can't hold a confirmed seat in coach. If I got the upgrade great, if not then I would get what was left in coach. I told her that this seemed to be a strange system and especially as the flight was full I would likely get stuck with a lousy seat in coach if I didn't get the upgrade. She shot back that I couldn't have my cake and eat it too, which I considered quite rude. Rather than battle it out (it had been a long day) I took my chances and needless to say got stuck in a middle seat in E- for the flight and was not a happy camper.

Is this really the way the upgrade system works or was something funny going on here?