4acee99 created the issue

• I am using a borrowed computer.
• I create a new connection via "Open Connection" and enter the SSH login details.
• The "Add to Keychain" checkbox is checked; I uncheck it.
• I connect and use the connection.
• I interrupt a file transfer; the connection drops.
• I click "Refresh".
• The connect dialog comes up again.
• "Add to Keychain" is checked.
• Without unchecking it for a second time (only happens if I notice), the credentials will be stored in the Keychain on this borrowed computer.

This is a new, default setup of Cyberduck and installed a few minutes ago, no prefs changes whatsoever, no bookmarks created.

I think that the default of adding to keychain, while convenient, should not reappear for a reconnected connection, and probably should not be the default for security reasons.