Description:
------------
Usually $this cannot be set. But by creating a reference to $this it can.
In the example the reference is created by the =& operator. The problem is also valid when passing $this to a function by reference.
I think an error should be generated because both $this = 1 and $this =& $x do generate an error.

Reproduce code:
---------------
class testclass
{
	function foo()
	{
		var_dump($this); // object(testclass)#1 (0) { }
		$this->bar();
		var_dump($this); // object(testclass)#1 (0) { } 
	}
	function bar()
	{
		$a =& $this;
		$a = 1;
		var_dump($this); // int(1)
	}
}

$b = new testclass;
$b->foo();

Expected result:
----------------
Fatal error: Cannot re-assign $this in eval()'d code on line 12

Actual result:
--------------
object(testclass)#1 (0) { }
int(1)
object(testclass)#1 (0) { }