IPageRendererProvider - HTTP 500 issue

Hi,

We had the requirement that we needed to use RedirectPolicy.NEVER_REDIRECT for
a single page in our app .
We used this code:

setPageRendererProvider(new IPageRendererProvider() {

@Override

public PageRenderer get(final RenderPageRequestHandler context) {

return new WebPageRenderer(context) {

@Override

protected RedirectPolicy getRedirectPolicy() {

RedirectPolicy result;

if (!((WebRequest) RequestCycle.get().getRequest()).isAjax()

& context.getPage() instanceof ExternalShareDocumentPage) {

result = RedirectPolicy.NEVER_REDIRECT;

} else {

result = super.getRedirectPolicy();

return result;

};

});

This seemed to work fine. However we made it live in production and we
noticed that we where getting "HTTP Status 500 - Cannot call sendRedirect()
after the response has been committed" a lot. It seemed to happen with a
flow like the following which was nothing to do with the
ExternalShareDocumentPage
tweak:

User clicks on link which does a setResponcePage(foo1.class)
in the constructor of foo1.class there is:
if (certainCondition) {

throw new RestartResponseException(foo2.class)

What I don't understand is why this is happening. It seems that by setting
the PageRenderProvider the way the redirects/commit seems to change.
Any ideas?