If in my page, I declare this event handler :
<f:event type="preRenderView" listener="#
and I do Ajax requests in the same view, the handler (init) is called for each ajax request (ok), but as many times as the number of Ajax requests made since the initial display of the page. For instance, if it is the 10th ajax request, for this request the handler will be called 10 times (in one RENDER VIEW phase); for the next request, if will be calles 11th times.
I've found a workaround : if I add <f:viewParam name="dummy"/> just before the event declaration, the preRenderView event is only fired once (for each ajax request)