Error file from import shifts headings over by 1 column

Whenever you import contacts and get an External ID duplicate error, you can download the file but it's adding an extra blank cell in the heading fields causing the field names to be shifted to the right.

In addition, why does the External ID have to be unique? In the old system, I ended up splitting apart people because CiviCRM handles Individuals so much better. I would like to tie both the husband and wife back to the original record.