I recently flew ORD-FRA on UA, FRA-ZRH on LH, ZRH-BRU on LX and BRU-ORD on UA, on 016 stock. I upgraded the middle two segments with LH miles (which cleared immediately), and the outer two with UA miles (waitlisted).

When BRU-ORD cleared, I called, and United resynced ("sunk") the ticket. This caused both partner upgrades to be lost - and indeed, the whole LX segment disappeared. I spent a good 45 minutes on the phone while several agents worked to fix this. Eventually I got the *A Upgrade desk, and he told me the following:

• This happens (upgrades are lost) when tickets are re-synced. It is best to leave them out-of-sync.
• LH had me in both B and I (their version of R) when this happened, and LX had me only in I. Both segments in I vanished, so I was left without anything on Swiss.
• They were able to re-upgrade me, but only because there was still I inventory. Otherwise I would have been out of luck.
• Reservations agents are not taught how to handle this. He was kind of annoyed at this, seeing as how he ends up having to fix these problems.

So the moral of this story is to be very careful with re-syncing a ticket if you have any partner upgrades. Tell the agents to call the *A upgrade desk to get instructions before you let them "fix" anything.