Quote - I left all of the Import and Export Options checkboxes and values at their defaults. For example, "Weld body part seams" and "Include body part names in polygon groups" are the only ones checked in the Export Options. Am I missing something?

On import, nothing should be checked.
On Export, you need only "Include existing groups in polygon groups".

Don't overwrite the original OBJ file when you export, especially when you've used the wrong options.