Doesn't seem like a duh moment. My guess is there is another factor at play. Typically for 4X3 material PAR should remain 4X3 from source to DVD. Sequence settings? DVD player settings? TV auto compensating?
Should I always be exporting at square pixels?
Only for web playback. For any kind of TV playback, use the correct PAR settings for your footage. The image will not be cropped at all (assuming you haven't applied any type of crop effect). If it appears cropped on your display, something else is going on.