I've actually been using 1Password for five years now and some of my machines used the older synchronization system with Dropbox. One of the bugs I've encountered is that even if you disable these synchronizers, the password on the Mac version of 1Password stays stuck on the old password in those shared storage systems.

Even deleting 1Password as an application doesn't help, so for a year or so, I've had to remember the older passwords to access my old machines.

Well, turns out that you have to completely delete all signs of 1Password from your machine. It is not just the plist (preference list), but basically, it is everywhere:

1. You actually don't have to delete the application itself, just the configuration programs. But you should quite completely out of it. There is an icon in the menu bar.
2. ~/Library/Application Support/ and delete anything named 1Password there.
3. ~/Library/Preferences and delete anything named agilebits there.
4. ~/Library/Containers and delete anything named agilebits there.
5. ~/Library/Group Containers and agilebits there as well.
6. Restart your Mac

Of if you are a power shell junky, this will do it:

rm -r "~/Library/Applications Support"/*1Password*
rm -r ~/Library/Preferences/*agilebits*
rm -r ~/Library/*Containers*/*agilebits*