Ranpre,
Sorry for the delay in this. We're looking into the issue and will hopefully have a solution soon.
One thing to note that may also work for you is the new feature in JFBConnect v6 that lets the user go through the standard JomSocial registration flow instead of the JFBConnect registration page. You can use that to use the JomSocial flow, while still having the profile information pre-filled for the user.
To try that, in the JFBConnect -> Configuration area, set the "Registration Component" to "JomSocial".
I hope that helps, but if not, let us know. I'm not sure how long the checkbox issue will take to fix, but will keep you posted if we don't hear back from you first.
Thanks,
Alex