Ahhh. That's excellent information. It's very true that that is what would be used as the login name/password because that's how our authentication plugin knows that the user is really logging in through Facebook. It's a little trick we play on the system, but I can see how it affects other plugins that are snooping the login information.
Let us know what your developer finds out, and we'll do some testing on our end with jFusion and PHPBB. It won't be an immediate fix, but if we can come up with a better authentication method that improves this situation, we're all for it. About once every other month, someone runs into an issue with jFusion (and they always seem different depending on what they're 'fusing' with), so we'd love to eliminate those conflicts.
Thanks, and keep us posted. We'll do the same.