Accessibility and possible Gnat bug

["Michael B." <michaelb@example.com>]

In the previous discussion about accessibility I was pointed to the 
paper "Accessibility rules OK!" of John Barnes (ACM SIGAda Ada Letters 
Volume XV Issue 1, Jan./Feb. 1995) which contains the following example:

procedure Example6  is
    type T is new Integer;

    procedure P1(XP1 : access T) is
       type A is access all T;
       Ptr: A := null;

       procedure P2(XP2: access T) is
       begin
          Ptr := A(XP2);
       end P2;

    begin
       P2(XP1);
    end P1;

    X : aliased T;

begin
    declare
       Y : aliased T;
     begin
       declare
          Z : aliased T;
        begin
          P1(X'Access);
          P1(Y'Access);
          P1(Z'Access);   -- Raises Program_Error.
        end;
     end;
end Example6;

In the paper the program is expected to run without errors.
I compiled it with Gnat 4.9 on Debian 8.0, ran it and got an 
Program_Error on the marked line.

Is this correct in Ada 2012 or not? I would like to hear your opinion 
about that before I write a possibly unnecessary bug report to AdaCore.

Regards,

Michael