Transitive inclusion of sequences breaks default instantiation

[senier]

The following reproducer

package Test is

   type U8  is mod 2**8;

   type M1 is
      message
         F1 : U8;
         F2 : Opaque with Size => F1 * 8;
      end message;
   type M1S is array of M1;

   type M2 is
      message
         F1 : U8;
         F2 : M1S with Size => F1 * 8;
      end message;

   type M3 is
      message
         F1 : M2;
         F2 : U8;
         F3 : M1S with Size => F2 * 8;
      end message;

end Test;

creates uncompilable code:

rflx-test-m3.ads:16:83: unmatched actual in instantiation of "Generic_M3" declared at rflx-test-generic_m3.ads:17                                                            
gprbuild: *** compilation phase failed