Just updated my galaxy note 10.1, and he same thing happened to me. Did you solve the problem, somehow?
I recently got my hands on a samsung allshare dongle, and it has worked as expected. I mainly use it to watch movier on my 32" HDTV, from my Galaxy III. On Netflix it used to show a fullscreen 16:9 ratio, however, after upgrading the S3 to 4.1.1 (from 4.0.?) it no longer shows a widescreen picture, but a letterbox format. Can't find any setting or such anywhere, any recommendations?