I downloaded the updated version and my contact list is filled with every address 1st name/last name as well as last name/1st name. Do I need the old version?

I always file my email contacts by last name first, and first name last. However after downloading the latest version I am getting both listings in my address book. I spend time deleting every duplicate that showed first name first, and last name last. But when I logged out and logged back into the software all the email addresses re-appeared. Do I need to go back to an older version of Thunderbird?