I locked a journal and now I can unlock it without a password!
This is because the password is stored in the Mac OS X Keychain. When you set the password originally you selected the "Save in Keychain" checkbox. If MacJournal can access your Keychain without having to bother you it can unlock the journal automatically. You either need to change your Keychain settings so the Keychain password is required to access it or delete the MacJournal items entirely. You can do either from the Keychain Access application in the Utilities folder.