iOS simple app: Form>Panel>TGridPanelLayout and Form>Button

iOS simple app: Form>Panel>TGridPanelLayout and Form>Button

procedure TForm1.Button1Click(Sender: TObject);
begin
  Panel1.DeleteChildren;
end;

==> error access denied in FMX.Layout.pas in TGridPanelLayout.TRowCollection.Notify 

any workaround?