Assignment access type with discriminants

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

I stumbled on a curious fact.

The value of an object with a discriminant can be changed to a value 
with a different discriminant if the type's discriminants are defaulted.

Right?

Wrong! Not through an access type!

procedure Test is
    type F is (F1, F2, F3);
    type Foo (K : F := F1) is record
       case K is
          when F1 =>
             X1 : Integer;
          when F2 =>
             X2 : Float;
          when F3 =>
             X3 : String (1..2);
       end case;
    end record;
    type Foo_Ptr is access all Foo;
    X : aliased Foo;
    P : Foo_Ptr := X'Access;
begin
    X := (F2, 1.0);   -- OK
    P.all := (F1, 3); -- Error!
end Test;

Is this a compiler bug or intentional language design? Any language lawyers?

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de