ODD Permalink Issue

I have a basic WordPress CMS/Blog setup with a custom homepage and blog page under Settings->Reading

Permalink Structre is setup as this:
“/blog/%postname%/”

I can go to page I created in WordPress such as http://www.example.com/pagename/, however when I am debugging my URL’s to make sure the URL structure is SEO friendly I have tried typing in http://www.example.com/blog/pagename/ to see what happens.

This URL is 302 redirecting to http://www.example.com/pagename/ because it recognizes it as a page not a post. Why is this not responding to a 404 header(or atleast 301 redirecting)?

What is the solution for users that use WordPress for large scale cms’ with hundreds of pages? Do they need to manually 301 redirect these urls as they create new pages?