I can tell you that the AV Wizard always says 4:3 on the final screen, so its not that ... coincidence... I know confusing, don't know why it does that, but always has for me in every version. Perhaps due to the way TV widescreen is transmitted inside a 4:3 timing window, but hardly self explanitory.
Perhaps your display mode timings are screwed up. You didn't say how you are connecting to, and what your display is. If it is VGA, DVI or HDMI, you could try turning on EDID in your xorg file. Or perhaps looking up your display on the Myth modeline database and creating a custom one. Finally, take a looking at your /var/log/xorg.0.log file as this may give some clues in the warnings or errors. Either way we need more info before we can help further.