Nothing. It's anamorphic as you said. It's for the display application to correctly display it. The question is really why you're exporting and where you're trying to get to. If the problem is in the QT player go to movie properties and set the Presentation aperture to Clean.
All the best,
Class on Demand DVDs "Complete Training for FCP7," "Basic Training for FCS" and "Final Cut Express Made Easy"
Author: "Final Cut Pro 5 Editing Essentials" and "Final Cut Express 4 Editing Workshop"