@HistoryPopState called multiple times

Steps to Reproduce

run the example multiple-historyPopState.zul
click the button a few times (pushes browser history states)
navigate back
observe the server logs

Current Result

the method handleHistoryPopState is called multiple times for the same history pop state event

Expected Result

handleHistoryPopState called once

Debug Info

the number how often the method is called corresponds to the number of root components on the page

Workaround

listen to onHistoryPopState with a @Command binding

	<div viewModel="@id('vm') @init('zk.support.BrowserHistoryVM')"
		onHistoryPopState="@command('handleHistoryPopState')">
        ...

	@Command
	public void handleHistoryPopState(@ContextParam(ContextType.TRIGGER_EVENT)
                           final HistoryPopStateEvent event) {
		final Object state = event.getState();
		System.out.println(state);
	}