Here are two classes:
<?php
class myBase
{
    function g()
    {
        return 'haha';
    }
    function output()
    {
        $x = new myBar($this);
        echo $this->g();
    }
}


class myBar
{
    var $container;
    function myBar(&$obj)
    {
        $this->container = $obj;
    }
}

// this work
echo myBase::g();        
?>


But when I copy the code of myBase::output() method outside the class defination, without changing the reference to $this variable passed to '$x = new myBar($this)' carelessly, that is

<?php
$x = new myBar($this);
echo myBase::g();   // this issue warning
?>

PHP gives a message to me:
Warning: Problem with method call - please report this bug in xxx on line xx

It should not be a normal case to work with $this outside a class, but as the message 'define' this as a bug, I just drop a message here.

:)