使用idudpserver和idudpclient编写的程序出现奇怪问题,请高手指点

这是两个很简单的测试udp 传输的程序,结果:
当client发送消息后,监听程序只能收到一半消息(例如:8条受到4条)
请高手看看,是什么问题:
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server(监听部分如下):
(监听端口和ip都已经设好)
unit Unit1;interfaceuses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, IdBaseComponent, IdComponent, IdUDPBase, IdUDPServer,
  ComCtrls,IdSocketHandle;type
  TForm1 = class(TForm)
    IdUDPServer1: TIdUDPServer;
    Label1: TLabel;
    Memo1: TMemo;
    Button1: TButton;
    Button2: TButton;
    StatusBar1: TStatusBar;
    procedure Button1Click(Sender: TObject);
    procedure Button2Click(Sender: TObject);
    procedure IdUDPServer1UDPRead(Sender: TObject; AData: TStream;
      ABinding: TIdSocketHandle);
  private
    { Private declarations }
  public
    { Public declarations }
  end;var
  Form1: TForm1;implementation
  {$R *.dfm}procedure TForm1.Button1Click(Sender: TObject);
begin
   IdUDPServer1.Active:=TRUE;
   StatusBar1.SimpleText:='Server is listening on port 39213';
end;procedure TForm1.Button2Click(Sender: TObject);
begin
   IdUDPServer1.Active:=FALSE;
   StatusBar1.SimpleText:='Server is down!'
end;procedure TForm1.IdUDPServer1UDPRead(Sender: TObject; AData: TStream;
  ABinding: TIdSocketHandle);
var ReceiveData :string ;
var SendData :string;
var VPeerIp  : string;
var VPeerPort : integer;
 begin
   ReceiveData:=IdUDPServer1.ReceiveString(VPeerIp,VPeerPort,-1);
   Memo1.Lines.Add(ReceiveData);
   Memo1.Lines.Add(VPeerIp);
   Memo1.Lines.Add(inttostr(VPeerPort));end;end.-----------------------------------------
client(发送端):
注: idudpclient的port和host 都设好了.
unit Unit1;interfaceuses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, ExtCtrls, IdBaseComponent, IdComponent, IdUDPBase,
  IdUDPClient;type
  TForm1 = class(TForm)
    Bevel1: TBevel;
    Label1: TLabel;
    Memo1: TMemo;
    Button1: TButton;
    Memo2: TMemo;
    Label2: TLabel;
    Label3: TLabel;
    IdUDPClient1: TIdUDPClient;
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;var
  Form1: TForm1;implementation{$R *.dfm}procedure TForm1.Button1Click(Sender: TObject);
var  SendData :string;
begin
     SendData:=Memo1.Lines.Text;
     idUDPClient1.Send(SendData);end;end.
请哪位高手帮忙解决,谢谢!