Sounds to me like the problem is that you are logging out of your apps
"local" account but not out of the Facebook session. Then when the
next page is loaded and the FB Connect init code runs again, it sees
you are still logged into Facebook and logs you in to your "local" app
account as well.
Try changing your logout link to use the facebooker helper like this:
fb_logout_link 'Logout', logout_path
instead of just doing a normal:
link_to 'Logout', logout_path
the fb_logout_link will log you out of both your "local" app and
Facebook.