Description:
------------
PHP allows invocation of an instance method in a class that
is unrelated to the current class. I would think that the
correct thing to do in this case is to generate an error
at runtime when this specific case is detected.

Reproduce code:
---------------
class One {
  function foo() {
    $isnull = ($this == NULL) ? "TRUE" : "FALSE";
    $instanceof = ($this instanceof One) ? "TRUE" : "FALSE";
    print "One::foo is \$this null ($isnull) : is instanceof One ($instanceof)\n";
  }
}

class Two {
  function foo() {
    $isnull = ($this == NULL) ? "TRUE" : "FALSE";
    $instanceof = ($this instanceof Two) ? "TRUE" : "FALSE";
    print "Two::foo is \$this null ($isnull) : is instanceof Two ($instanceof)\n";
    return One::foo();
  }
}

$obj = new Two;
$obj->foo();


Expected result:
----------------
When executed, PHP prints:

Two::foo is $this null (FALSE) : is instanceof Two (TRUE)
One::foo is $this null (FALSE) : is instanceof One (FALSE)

It should generate an error here since Two is unrelated
to class One. This check should be done when invoking
the instance method, if the $this ref is not NULL then
the type of $this should be checked before the instance
method can be invoked in One.

I already read bug 42559, it seems to have been rejected
as "not a bug", but this issue is clearly a bug. Use of
a method call like CLASS::METHOD inside a class def does
not mean the method being invoked is static.