Threads

Hello!
    I have create this simple thread class, I am posting down below, but
I can't understand why it does not work right. It simply shows  a form
and update its caption with the current time.
    If I fire two istances of the same thread and two istances  of the
same form, one of those forms is not updated (I don't see seconds running).
    If I change the left property of to one of the forms, before showing
it, everything seems to work fine. But if I move  one form  with the
mouse one form (not always the same) stop updating.  Where am I wronging?

thanks
Marco

procedure TForm1.Button2Click(Sender: TObject);
begin
   with TThrd.Create(true) do
   begin
     aForm := TForm2.create(self);
      FreeOnTerminate:= true;
     Resume;
   end;
   with TThrd.Create(true) do
   begin
     aForm := TForm2.create(self);
     FreeOnTerminate:= true;
     Resume;
   end;
end;


   TThrd = class(TThread)
   private
     Flbl: TLabel;
     FForm: TForm;
   protected
     procedure Execute; override;
     procedure VisualUpdate;
   public
     property aLbl: Tlabel read Flbl write Flbl;
     property aForm: TForm read FForm write FForm;
   end;
...
procedure TThrd.Execute;
begin
   Synchronize(aForm.Show);
   repeat
     Synchronize(VisualUpdate);
   until Application.Terminated;
end;

procedure TThrd.VisualUpdate;
begin
   aForm.Caption := FormatDateTime('hh:nn:ss', now);
   aForm.Update;
   application.processMessages;
end;