user.php logout - headers already sent

[keg01]

Version: 1.0.0
Template: wistie (though it seems to occur with any)

I stumbled on a behavior I haven't been able to isolate to a root cause. When viewing the "Profile" page (user.php) and logging out, the user receives the following warning:

"Warning: Cannot modify header information - headers already sent by (output started at /public_html/user.php:1) in user.php line 72"

Logging from any other page does not cause an issue.

This line is the header that redirect the user (see below, header('Location: ./') after logging out as below.

 // if not logged in, redirect to the index page
        $login = isset($_GET['login']) ? sanitize($_GET['login'], 3) : '';
        $truelogin = isset($_COOKIE['mnm_user'] ) ? sanitize($_COOKIE['mnm_user'] , 3) : '';
        if($login === ''){
                if ($current_user->user_id > 0) {
                        $login = $current_user->user_login;
                } else {
                     header('Location: ./');
                        die;
                }
        } 
  

Not sure what headers are already being sent in this use case and I hope someone can isolate it.

To recreate the issue:

1. Log in
2. Click on the link, "Profile"
3. Click on the link, "Logout"

[keg01]

File this one under, "Gave up to quickly." The root cause was core file customization in user.php. Case closed.