Ada 95 visibility question

[Tom Moran <tmoran@bix.com>]

Of three compilers I tried this on, 2 took it happily and one said it
couldn't find such a thing as "peek_a_boo" at the place indicated. 
What's correct?
package c is
  type root is tagged private;
private
  type root is tagged record
    peek_a_boo:integer;
  end record;
end c;

package c.d is
  type dialog is new c.root with private;
private
  type dialog is new c.root with record
    dd:integer;
  end record;
end c.d;

with c.d;
package c.f is
  type file_dialog is new c.d.dialog with private;
  procedure p(x:in out file_dialog);
private
  type file_dialog is new c.d.dialog with record
    ff:integer;
  end record;
end c.f;

package body c.f is
  procedure p(x:in out file_dialog) is
    y:integer;
  begin
    y:=root(x).peek_a_boo;
    y:=x.peek_a_boo;  1/3 of compilers tested complained
  end p;
end c.f;

with c.f;
procedure bug1 is
  f:c.f.file_dialog;
begin
  c.f.p(f);
end bug1;