Twitter can't fix this, unless the FB application is only using Twitter's authentication system to ensure it's properly linked. Facebook twitter apps can just

Twitter can't fix this, unless the FB application is only using Twitter's authentication system to ensure it's properly linked. Facebook twitter apps can just scrape twitter for your most recent status update -- if that's the case, they don't even need your twitter password to get updates. (I don't know how that twitter->facebook app works, but given your situation, that's what I'd guess. So there isn't anything Twitter could do to stop it.)