The issue: Implementing singleton pattern
<?php
class Singleton {
    private static 
$instance;
    public static 
$static 42;
    public 
$property;

    private function 
__construct() {
        
$this->property microtime();
    }

    public static function 
getInstance() {
        if (!isset(
self::$instance)) {
            
self::$instance = new Singleton();
        }
        return 
self::$instance;
    }
}

var_dumpSingleton::getInstance() );
var_dumpSingleton::getInstance() );
?>
Output
object(Singleton)#866 (1) { ["property"]=> string(21) "0.04797200 1731639908" } object(Singleton)#866 (1) { ["property"]=> string(21) "0.04797200 1731639908" }
PHP 4 could only simulate a singleton with global variables.
Static properties may be accessed without a class instance.
<?php
var_dump
Singleton::$static );
?>
Output
int(42)