I flew PDX-ATL-MUC last night, upgrading an M to a Z fare with a PMU. When checking in to the ATL BE lounge the agent told me that BE on the ATL-MUC leg was oversold and that they might have to put me "in the back." I said, no way. I had my upgrade confirmed since July, and I also had a BP printed five hours earlier clearly stating my BE seat assignment. On top of that, I had bought a M fare specifically with the intent to upgrade, and I had "paid" for the upgrade with a PMU. The agent was very pleasant (and so was I), and in the end it worked out fine, but I'm a bit shocked to hear that DL would be able to downgrade previously upgraded tickets just like that. It also seems to be a pretty poor way to treat your supposedly best customers.

I wonder: Could the agent have downgraded me? What kind of remedies would there have been? I would assume getting the PMU back would be a minimum, but then there's also the issue of having purchased a M vs. LUT fare. Any input appreciated...