If it makes no difference using a few different web pages then I would suggest something radical here...

It would only take a few minutes but try rebuilding the app but with the minimum of code. So open a new project, place a WebBrowser on the form and a button. In the button click event put
WebBrowser1.Navigate("http://www.google.com"),
in the load event put
WebBrowser1.Navigate("http://www.cnn.com").

Does that exhibit the exact same behaviour? If it doesn't then perhaps your existing project is in some way corrupted or there is a property set wrong somewhere.