Comments Plus ignores Facebook login

I'm using Comments Plus and can happily get Wordpress, Twitter & Google to work perfectly. But try and try again I can't get Facebook to work.

When I try to login to facebook in the comment field it just throws me to the top of the current page and does nothing.

here's a test page showing what happens:
http://test.toptasmania.com/2011/11/shortcode-test-2/

Thoughts? I'm sure I've set the app up OK....