I don't know if it is the same bug as this one: http://bugs.php.net/bug.php?id=22231&edit=2

<?php
class foo {
    function bar() 
    {}
}

function &foo() {
    $GLOBALS['foo'] =& new foo;
    return $GLOBALS['foo'];
}

/* 
The following lines cause a warning:
Problem with method call - please report this bug
*/
$foo =& foo();
$foo->bar('value');
unset($foo);

/*
A method call without a value does not cause the warning.
*/
$foo =& foo();
$foo->bar(/* no value */);
unset($foo);

/*
But the two lines together cause a fatal error:
Call to a member function on a non-object
*/
$foo =& foo();
$foo->bar(/* no value */);
$foo->bar('value');        // the error occurs in this line!
unset($foo);

?>