Ada 2012 and type access to in out functions

[David Sauvage <david.sauvage@adalabs.com>]

Using GNAT GPL 2011, I try to define a type that is an access to an in
out function, and the following example code [1] is illegal for the
compiler.

Is it an Ada 2012 restriction on using in out functions, a GNAT GPL
2011 limitation or a bug ?

Cheers,

[1]
-- gnatmake -gnat12 in_out_function_access_type.adb
procedure In_Out_Function_Access_Type is

   function Validate (Status : in out Boolean) return String
   is
   begin
      Status := True;
      return "command";
   end Validate;

   type Callback is access function (Status : in out Boolean) return
String;
   -- illegal  functions can only have "in" parameters.
   -- build successfully if the above line is commented
begin
   null;
end In_Out_Function_Access_Type;