not able to handle JSF render exception - jsf-2

Question

Using mojarra 2.1.27 and richfaces 4.3.6 on tomcat7, I was trying to implement my own exception handler for the ajax requests (Following all your advices) but I never get access to the render exception.
I have normal postback exceptions handled through web.xml <error-page> directives, which works fine, and ajax request should go through my custom handler. This seems to work when updating values and invoking the actions, but not with exceptions during rendering phase.
Having this simple ajax command button
<a4j:commandButton execute="#this" action="#{testController.actionButton4}"
render="#form" value="Ajax Post + Render Error"/>
which (amongst others) renders a div with a result
<div id="result">
#{testController.result}
</div>
Is backed by a simple action in my TestController
public String actionButton4() {
result = "action4";
inError = true;
return null;
}
And a simple getter which is used during the render.
public String getResult() {
if (inError) {
inError = false;
throw new RuntimeException("Render error in " + result);
}
return result;
}
My handler does more or less the default behaviour
public void handle() throws FacesException {
dohandle();
getWrapped().handle();
}
public void dohandle() throws FacesException {
FacesContext fc = FacesContext.getCurrentInstance();
PhaseId phaseId = fc.getCurrentPhaseId();
boolean partialRequest = fc.getPartialViewContext().isPartialRequest();
boolean ajaxRequest = fc.getPartialViewContext().isAjaxRequest();
Iterator<ExceptionQueuedEvent> iterator = getUnhandledExceptionQueuedEvents().iterator();
log.trace("Phase id ({})", phaseId);
while (iterator.hasNext()) {
log.trace("Request is partial ({}). Request is ajax ({})", partialRequest, ajaxRequest);
if (!ajaxRequest) {
return;
}
...
}
}
What I see during rendering is a logging exception in the ExtendedPartialViewcontextImpl of richfaces
Jun 25, 2014 10:18:44 AM org.richfaces.context.ExtendedPartialViewContextImpl$RenderVisitCallback logException
SEVERE: /test2.xhtml: Error reading 'result' on type c.n.g.w.controller.TestController
...
Then I see the phase ends and the exception handler is consulted
10:18:44.336 {http-bio-8080-exec-2} TRACE c.n.g.w.generic.LifeCycleListener - END PHASE RENDER_RESPONSE 6
10:18:44.336 {http-bio-8080-exec-2} TRACE c.n.g.w.generic.ExceptionHandler - Phase id (RENDER_RESPONSE 6)
But for some reason there is no unhandled exception in the queue.
I couldn't find anything stating that the RF rendering should react any different that others, but I suspect it could be. Does anyone know more than me here?
UPDATE:
I notice from the client side log that the rendered output is clipped right at the EL tag, so the rendering breaks and commits the partial result for some reason.