Go back to edit this address and you'll see it's now the default.
Edit the first address but save without actually making any changes - it'll become the default.
It looks like the default was perhaps specified with a checkbox rather than radio in a previous version??? To fix, open up 'catalog/model/account/address.php and replace both occurences (lines 8 and 18) of:
Code: Select all
if (isset($data['default'])) {
Code: Select all
if ($data['default'] == "1") {