IndicatingAjaxButton should have construtors that take a IModel for the button text as does AjaxButton.

IndicatingAjaxButton is missing the constructors that take an IModel for the button text that AjaxButton supports.

public IndicatingAjaxButton(String id, IModel<String> model)
public IndicatingAjaxButton(String id, IModel<String> model, Form<?> form)

I think IndicatingAjaxButton should offer the same API as AjaxButton.