Unless you login with a FaceBook developer account, it seems that we can not login with Sencha.IO using Facebook as the auth.
The Sencha Touch IO app redirects to FaceBook ok (after pressing 'Login with facebook' button), the FaceBook login works as you would expect, and you get redirected back to the app, as you would expect.
However, if you logged in with FB credentials that are not linked to a FB developer account, then the Sencha Touch app redirects back to the 'Login with Facebook' button. It works if you login with a FaceBook developer account? Why?!