If your code doesn't match the SQL query listed above, here is what to do.
In admin/order.php, change this line:
Code:
db_query("update $sql_tbl[orders] set tracking='$tracking', notes='$notes' $details where orderid='$orderid'");
To this:
Code:
db_query("update $sql_tbl[orders] set tracking='$tracking', shipping_vendor='$shipping_vendor', notes='$notes' $details where orderid='$orderid'");
Works great!