Brain bug or GNAT bug?

["(see below)" <yaldnif.w@blueyonder.co.uk>]

Using GNAT GPL 2006 (PPC/Darwin), I instantiate:

   generic
   
      type modular is mod <>;
   
   package try is
   
      type DT1 (the_size : modular)  is limited private;
   
   -- subtype bounded is modular;
      subtype bounded is modular range 1..9;
      type DT2 (the_size : bounded)  is limited private;
   --                         |
   -- >>> subtype must be compatible with parent discriminant
   
      function is_empty (the_data : DT2) return Boolean;
   
   private
   
      type a_thing is null record;
      type a_ptr   is access a_thing;
      
      type a_ptr_array is array (modular range <>) of a_ptr;
   
      type DT1 (the_size : modular) is
         record
            things : a_ptr_array (1 .. the_size);
         end record;
   
      type DT2 (the_size : bounded)  is new DT1(the_size);
   
   end try;

and I get the error message commented-out at line 11.

If I substitute the declaration at line 9 for that at line 10,
the test program compiles and runs correctly.

Am I blundering here, or is this a GNAT bug?

-- 
Bill Findlay
<surname><forename> chez blueyonder.co.uk