Facebook SSO authorize in safari but not facebook app in my iphone

I am following the guide exactly开发者_如何学运维 to integrate with Facebook. A weird issue that i run into is that, if I,

1. uninstall the facebook app in iphone

2. OR change the facebook.m implementaion to disable facebook app like [self authorizeWithFBAppAuth:NO safariAuth:YES];

The authorize method works well in safari and get back the auth token in the url

However, if I am not doing the above 2, it will switch to facebook app, and after it says 'loading...' for a second, it gets back to me an url saying user denied. (fbxxxxxxxxxxxxx://authorize#error_reason=user%5Fdenied&error=access%5Fdenied&error_description=The%2Buser%2Bdenied%2Byour%2Brequest%2E%3F%5F)

Why it behaves so differently in the native app and browser? Is it a bug in FB iPhone app? I am using the same app and same user to test.

double check your iOS Bundle ID in facebook app setting, it has to be exact same as what you define in app.