Ming,
The comment box is appearing twice because you're using another Facebook Comments plugin (or something) in addition to JFBConnect. We're only inserting it once. If you want to use our box (which we recommend since it's using the new Comment Box method), you should disable or remove the other Comment plugin/extension you're using. I don't know what's adding that, but can probably help investigate further if you can't find it.
Hope this helps. I'm assuming the same other extension is adding the Share button as well, but again, that's not from JFBConnect.
Good luck!