Patrick,
Something in Joomla is caching it. I'm not sure what that would be though. If you clear the cache, that should update it.. but it sounds like you may have additional caching somewhere, but I honestly don't know where to look.
There's not anything in JFBConnect that would be caching the language string or override.
Sorry I can't help explain much more, but should you have any other questions, just let me know.
Thanks,
Alex