A bug in Gnat, or in my code?

["Björn Persson" <spam-away@nowhere.nil>]

This program, when compiled with Gnat 3.3.2 and run on Fedora Core 1, 
raises Storage_Error on line 7 (because of a segmentation fault):

procedure Error is                        --  1
                                           --  2
    procedure Proc (NullS : String) is     --  3
       type SA is access String;           --  4
       Point : SA := new String (1 .. 0);  --  5
    begin                                  --  6
       Point.all := NullS;                 --  7
    end Proc;                              --  8
                                           --  9
    S : String := "s";                     -- 10
begin                                     -- 11
    Proc(S(3 .. 1));                       -- 12
end Error;                                -- 13

If I change 3 to 2 on line 12 there is no error. As far as I can see, 
(3..1) should be as legal as (2..1).

Am I right that this is a bug in Gnat?

-- 
Björn Persson

jor ers @sv ge.
b n_p son eri nu