向高手请教, DELPHI变体取值不正确,是不是稳定性有问题

testrec = packed record
case Integer of
    0: (shi:Shortint);
    1: (b:Byte);

    2: (smi: Smallint);
    3: (w: WORD);

    4: (i: Integer);
    5: (dw:DWORD);

    6: (buff : array[0..3] of Byte);
end;

procedure TForm1.Button1Click(Sender: TObject);
var
    a : testrec;
begin
    a.i := -1;
    ShowMessage(IntToStr(a.shi));// -1
    ShowMessage(IntToStr(a.b));// -1
    ShowMessage(IntToStr(a.smi));// -1
    ShowMessage(IntToStr(a.w));// -1
    ShowMessage(IntToStr(a.i));// -1
    ShowMessage(IntToStr(a.dw));// 4294967295
end;