IContentRepository - Work after clearing cache

Hi,

Inspired by the this arcticle, I've created a setting page.

At first it worked perfectly but I noticed that at some point in time, the contentrepository return is null when I tryed to retreive the page:

 [AcceptVerbs(HttpVerbs.Get)]
public ActionResult GetSettings(DealerLocationRequestParameter parameter)
{
   var settings = _contentRepository.GetChildren(ContentReference.RootPage).FirstOrDefault();
   [...]
}

If I switch my web browser in private mode (or clean the web browser cache manually), it works again.

How can I fix it ? What is in cache that created this issue ?

Thanks,