TClientDataSet.CreateDataSet为什么出错

今天遇到一个怪问题，在Delphi中，运行如下程序，正常

unit Unit1;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, Grids, DBGrids, DBClient, DB;

type
  TForm1 = class(TForm)
    dbgrd1: TDBGrid;
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.FormCreate(Sender: TObject);
var
  TitleNames:array of String;
  I:integer;

  DStTemp: TClientDataSet;
  fldsTemp:array of TStringField;

  dsTemp:TDataSource;
begin
  Setlength(TitleNames,2);
  //  长度为31
  TitleNames[0] := '1234567890123456789012345678901';
  TitleNames[1] := '这是一个测试标题宽度的实验程序';

  DStTemp := TClientDataSet.Create(dbgrd1);
  SetLength(fldsTemp,2);

  for I:=0 to 1 do
    begin
      fldsTemp[I]:=TStringField.Create(dbgrd1);

      dbgrd1.FindComponent('Field'+IntToStr(I)).Free;
      fldsTemp[I].Name:='Field'+IntToStr(I);
      
      fldsTemp[I].Name:='Field'+IntToStr(I);
      fldsTemp[I].FieldName:=TitleNames[I];
      fldsTemp[I].Size:=10;
      fldsTemp[I].Index:=I;
      fldsTemp[I].DataSet:=DStTemp;
    end;

  DStTemp.CreateDataSet;
  {
    对DataSet赋值
  }

  dsTemp := TDataSource.Create(dbgrd1);
  dsTemp.DataSet := DStTemp;

  dbgrd1.DataSource := dsTemp;  
end;

end.

但是，当TitleNames[0]='12345678901234567890123456789012'，也就是说长度大于31的时候，就会发生错误，不知道为什么？？