Dirk,
There's a few ways to disable the Grammar filter that we've read about, but haven't really tested. If you could, let us know what version of JFBConnect you're using and how you're implementing the Comments (the content plugin to automatically add to articles, the module, or the {JFBCComments} tag).. that will help us come up with the best solution for your case.
Also, please post from the account you subscribed from. Priority support is for our subscribers.
Thanks!
Alex