[Alegun]

Получилось "харакири" через PostMessage

Код:

...
 protected
    procedure WndProc(var Msg: TMessage); override;
...

procedure TForm1.WndProc(var Msg: TMessage);
begin
  case Msg.Msg of
    CM_RELEASE: FreeAndNil(MB);
    else inherited;
  end;
end;

...
procedure TMButton.Click;
begin
  inherited;
  PostMessage(Form1.Handle, CM_RELEASE,0,0);
end;