Normal posts shown in custom post edit page

On my site http://www.myhifi.it, I created a custom post type and now, on admin pages, I can correctly see the link to the posts page and to the custom posts page.
When I click on the Posts page link I see only posts, but, when I click on the Custom Posts link I see custom and “normal” posts on the same page.
Why is this happening? How can I fix it?

http://wordpress.org/extend/plugins/custom-post-type-ui/