read from TMemoryStream fails

I want to use a stream for example for clipboard operations. If I read and write the stream within the same procedure (Button3Click) it occures successfull. If I split this procedure into the Button1Click+Button2Click procedures I loose in the line marked as {B} the value of RecordDestination.Wort. This value has been modified in a mysterious way at this point.
Up to now I have no expirience using streams. May be I'm wrong but I think it should be possible to to use streams in this way.


type
      TMyRecord = record
            Zahl: cardinal;
            Wort: String;
      end;

var
      Form1: TForm1;
      MyStream: TMemoryStream;

implementation

procedure TForm1.Button1Click(Sender: TObject);
var
      RecordSource: TMyRecord;
begin
  RecordSource.Zahl:=123;
  RecordSource.Wort:='BullShit';
    MyStream:=TMemoryStream.Create;
    MyStream.Clear;
    MyStream.Write(RecordSource,SizeOf(RecordSource));
end;

procedure TForm1.Button2Click(Sender: TObject);
var
      RecordDestination: TMyRecord;
begin
      MyStream.Seek(0,soFromBeginning);
      MyStream.Read(RecordDestination,MyStream.Size);
      MyStream.Free;
{A}   Edit5.Text:=IntToStr(RecordDestination.Zahl);
      Edit6.Text:=RecordDestination.Wort;
end;

procedure TForm1.Button3Click(Sender: TObject);
var
      RecordSource, RecordDestination: TMyRecord;
begin
  RecordSource.Zahl:=124;
  RecordSource.Wort:='Bulleye';
    MyStream:=TMemoryStream.Create;
    MyStream.Clear;
    MyStream.Write(RecordSource,SizeOf(RecordSource));
      MyStream.Seek(0,soFromBeginning);
      MyStream.Read(RecordDestination,MyStream.Size);
      MyStream.Free;
{B}   Edit5.Text:=IntToStr(RecordDestination.Zahl);
      Edit6.Text:=RecordDestination.Wort;
end;