Description:
------------
When this is run on PHP8.0 and older (7.x), the static $cache variable is set to [] on each instantiation but on 8.1 it still keeps the data from the previous instantiations. 

PHP8.1 test link https://3v4l.org/qLpoT#v8.1rc3
PHP7.4 test link https://3v4l.org/qLpoT#v7.4.26

<?php

abstract class Cache{
    protected function put($key,$value){
        static $cache = [];
        var_dump($cache);
        return $cache[$key] = $value;
    }
}

$instance1 = new class extends Cache{
    
    public function store($key,$value)
    {
        return $this->put($key,$value);
    }
};

$instance1->store("one",1);
$instance1->store("two",2);
$instance1->store("three",3);


$instance2 = new class extends Cache{
    
    public function store($key,$value)
    {
        return $this->put($key,$value);
    }
};

$instance2->store("four",4);
$instance2->store("five",5);


$instance3 = new class extends Cache{
    
    public function store($key,$value)
    {
        return $this->put($key,$value);
    }
};

$instance3->store("six",6);
$instance3->store("seven",7);