Problem with static variable from class that extends an abstract

Question

Why is this code outputting "third third third"?

<?php

abstract class xyz {

    static $var;

    public static function setVar($value) {
        static::$var = $value;
    }
}

class one extends xyz {}

class two extends xyz {}
class three extends xyz {}

call_user_func('one::setVar', 'first');
call_user_func('two::setVar', 'second');
call_user_func('three::setVar', 'third');

echo "<pre>";
echo one::$var."\n";
echo two::$var."\n";
echo three::$var."\n";
echo "</pre>";

I would have thought first, second third

What am I missing here?

Update

This was my resolution

public static function setVar($value) {
        $class = get_called_class();
        $class::$var =& $value;
    }