One the hard things about Facebook App development is debugging weird Facebook API issues.
One of them is the inconsistent use of the FB.Canvas Javascript methods. Particularly FB.Canvas.setAutoGrow and FB.Canvas.setSize. The documentation explains that (either or both?) can be used ad hoc to resize the app iframe. Well that’s not exactly the case, as neither work when called after the initial page load.
Although hacky, this solution actually works.