I upgraded 1Password Pro on my iPad before I saw that I had to upgrade my Mac as well for sync to work. This manifested in the expected way - enter DropBox login details on the iPad, no data found.
However once I had upgraded my Mac, I reloaded 1P on the iPad and all it could say was "master password incorrect". This was very strange as it had never actually asked me for my dropbox keychain's master password!
Eventually I discovered the option to re-enter my master password and everything is good now, but that's definitely confusing
(Also worth noting, my master password on the DropBox keychain was the same one I'd just entered to open the iPad app thanks to previous WiFi sync. I thought it was supposed to use that before asking? Maybe related to the fact it never asked?).