Thanks. I just registered, and I got the proxymail.facebook address as well. We register on sites *a lot*, and I've haven't seen that address in at least a year (likely much longer).
I'm not sure why you're site is fetching that email, but we'll gladly help investigate further.
First, if you want a 'quick' test, I'd recommend trying to create a new Facebook Application. See if that one has the same issue. If so, that means it's something with your domain (possible) and/or site/JFBConnect (possible) and or/ server (very unlikely) configuration.
If that doesn't work, or you don't want to try the test above, please Private Message me a set of admin credentials, and I'll see what I can do. You can PM me by clicking the mail icon under my picture to the left.
Thanks,
Alex