Cannot disable ADD_SHEET option to prevent user to create a new "tab" (sheet).

@Override
public void doAfterCompose(Component comp) throws Exception {
Spreadsheet ss = (Spreadsheet) comp;
ss.disableUserAction(AuxAction.ADD_SHEET, true);
super.doAfterCompose(ss); //wire variables and event listeners
}

As you can see, I can click "+" button and create a new sheet "Sheet2".