Not sure if this is a bug or the desired behavior but apparently Facebook does not understand their own app-scoped user ID if it is used in a "article:author" meta tag. Debugging the page will yield an error that says the provided value (http://facebook.com/some-app-scoped-id/) is not a profile. Of course if you go to that url, it will redirect to the correct user profile page. It just doesn't work for sharing, probably for security reason. In our case, we have to let user enter their own username/id and use that for the meta tag. Not the best user friendly experience but it works for now...
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