[angvelem]

Нужно добавить обработчик :

Код:

  private
    { Private declarations }
    procedure WndProc(var Msg: TMessage);
...
procedure TForm1.WndProc(var Msg: TMessage);
begin
  if (Message.Msg = WM_SYSCOMMAND) and (wParam = SC_RESTORE) then
...
  inherited;
end;