Auto username problem

Hi, i’m using this plugin to auto generate username on registration:

<?php
/*
Plugin Name: Auto Generated numbered Username
Version: 1.0
Plugin URI:
Description: Simple WordPress plugin to automatically generate numbered username, hook in to wordpress user registration page and automaitcally add			 			 numbered Username in "Username" Field.
*/
	// global variable next username
	// @var $next_username
	global $next_username;	

	// global default variable starting username number
	// @var $starting_username
	global $starting_username;

	// Start from numbered username from 1001 if previous numbered username is not found in users table,
	// you can set this value to any number before adding any numbered username in database;
	$starting_username = 1001;

	// current page
	global $pagenow;

	// add jquery in head section of registration page
	if( $pagenow == 'wp-login.php' && $_REQUEST['action'] == 'register')
		add_action('init', 'add_scripts_method' );

	// hook in to user registration form

	add_action('register_form', 'add_default_username');

	// add in theme header
	add_action('wp_head', 'add_scripts_method' );
	add_action('wp_head', 'add_default_username');

	// add action hook to redirect new user add to edit profile page
	add_action("admin_init", "redirect_user_add");

	// check if which page we currently are in
	if( $pagenow == 'user-new.php')
		// add action to admin footer
		add_action('admin_footer',  'show_next_available_username' );	

	// Function to add numbered username in user registration page
	function add_default_username()
	{
			// get next username
			$next_username = get_next_available_username();

			 // add $next_username to user login field value in user registration form
			 // and this field to redonly so that user cannot changed using jQuery
			 ?>
             <script type="text/javascript">
             	jQuery(document).ready(
					function(){
						var username = '<?php echo $next_username; ?>';
						var message = '<p class="message register" style="padding:5px; margin:0 0 10px 0">Username is auto-generated and can not be changed.</p>'; // message
						jQuery('input[name="user_login"]').val( username );
						jQuery('input[name="user_login"]').attr('readonly', 'readonly');
						jQuery('label[for="user_login"]').after( message );

						/*** to work with wp profile builder plugin **/
						var message1 = '<label class="note" style="padding: 5px; margin: 0px 0px 10px; float: right; width: 65%; color: red;">Username is auto-generated and can not be changed.</label>'; // message

							jQuery('#wppb_register input[name="user_name"]').val( username );
							jQuery('#wppb_register input[name="user_name"]').attr('readonly', 'readonly');
							jQuery('#wppb_register input[name="user_name"]').after( message1 ); 

					}
				);
			 </script>
             <?php
	}

	// Display next available username in add new user page
	function show_next_available_username()
	{
		// add jquery
		add_action('wp_enqueue_scripts', 'my_scripts_method');

		// get next username
		$next_username = get_next_available_username();

		// display next available username using jqeury
			 ?>
             <script type="text/javascript">
             	jQuery(document).ready(
					function(){
						var username = '<?php echo $next_username; ?>';
						var message = '<p class="update-nag" style="width:24em; padding:5px; margin:5px 0">Next available Username #<strong>'+username+'</strong></p>'; // message
						jQuery('input[name="user_login"]').after( message );

						// add onsubmit attribute to form
						jQuery('form#createuser').attr('onsubmit', 'return checkUsername()');
					}

				);
				// auto add username if username field is blank
					function checkUsername()
					{
						var username = jQuery('input[name="user_login"]').val();
						if( username == '')
						{
							var username = '<?php echo $next_username; ?>';
							jQuery('input[name="user_login"]').val(username);
						}
						return true;
					}
			 </script>
             <?php
	}

	// function to get next available username
	function get_next_available_username()
	{
		// global DB variable/object
		global $wpdb;

		global $starting_username;

		// get all username/number from database
		$query = 'SELECT user_login FROM '.$wpdb->users;
		$usernames = $wpdb->get_col( $query );
		if( $usernames )
		{
			$i = 0; // starting array index
			$numeric_usernames = array();
			foreach( $usernames as $username )
			{
				if( is_numeric( $username ) )
				{
					$numeric_usernames[ $i ] = $username;
					$i++;
				}
			}

			 // check if numeric usernames are empty
			 if( !empty( $numeric_usernames ) )
			 {
				 // get the latest/maximum value of usernames
				 $last_username = max( $numeric_usernames );
				 $next_username = $last_username + 1;
				 return $next_username;
			 }
			 else
			 {
				return $starting_username;
			 }
		}
		else
		{
			return $starting_username;
		}
	}

	// redirect new user add to edit profile page
	function redirect_user_add() {
		if(!empty($_GET['update']) && $_GET['update'] == 'add' && !empty($_GET['id']) ) {
			$id = $_GET['id'];
			//$user = get_userdatabylogin($username);
			wp_redirect( admin_url("/user-edit.php?user_id=".$id ) );
		}
	}

	// enqueue jquery library
	function add_scripts_method() {
	    wp_deregister_script( 'jquery' );
		wp_enqueue_script( 'jquery', plugins_url('/jquery-1.7.1.min.js', __FILE__), array(), '1.7.1');
		wp_enqueue_script( 'jquery' );
	}
?>

I am facing a bit of a problem since if a user forgot his/her password, then a generated Number username automatically is added to the form.

Is there a way to correct this?
By the way, I’m usig classipress theme if that is important. I need auto username because of author pages, i don’t want usernames in url’s, number’s are better 😀