$wpdb->insert writes a record twice for some reason, when my custom developed plugin calls my class function once

Question

My custom code in my custom (class-based) plugin for some reason, writes the same record twice, when as you can see it's called once. This double write also happens even when I do the same type of insert into the wp_posts table, so it's not specific to the wp_users table. I'm baffled. Any ideas appreciated.

<?php
class InsertUserWP {

    function dbase_insert_wp_user() {
        global $wpdb;

        $wp_users_table = $wpdb->prefix . 'users';

        $newUser = $wpdb->insert(
            $wp_users_table,
            array(
                'user_login' => 'deleteme_login_' . rand(1, 10000),
                'user_pass' => md5('deletemmepass'),
                'user_nicename' => 'deleteme_nicename',
                'user_email' => 'mario' . rand(1, 10000) . '@email.com',
                'user_status' => 0
            )
        );
        echo 'new user ID is: ' . $wpdb->insert_id . '<br>'; // (returns the first ID on screen)
    }

    // call the above insert function
    function dbase_call_user_insert() {
        $this->dbase_insert_wp_user();
    }
}


// Run the insert
$insertCompanies = new InsertUserWP(); //instantiate the class
$insertCompanies->dbase_call_user_insert(); // run the insert function within