does that page included from some other or opened directly ? then add html-body structure and not use composition.
if included - doublecheck that you have no nested forms.
In that case it would be better to use just a4j:commandButton and not use ajaxSubmit=true. It was designed for the case when you have to use some existent components which works without ajax support and there are no alternatives.
it was included in a nested form that was useless, throwing that form it works great ;-)
Thanks a lot