JSF Bean is not called when in ajax mode
===

This code works :

    <h:commandLink value="#{episode.index}" action="#{fooBean.bar}">
    </h:commandLink>

but this one (the same with ajax) does not do anything :

    <h:commandLink value="#{episode.index}" action="#{fooBean.bar}">
       <f:ajax />
    </h:commandLink>

There is no error logged in the server side nor in the client side. The bean is just not called at all. I tried using f:ajax `listener` attribute instead of commandLink `action` attribute. I also tried to specify `execute` and `render` without success.

What could cause the bean method to not be called when ajax is used?