Last posts of a user

Normally I see in a user profile under the window “Statistics” and “Activity” a window with the last post of a user and also a link to show me all of his posts, below then another window with the signature. But there are also users there missing the window with the posts and you see only “Statistics”, “Activity” and “Signature” What is wrong? If I take the URL to the post display of another user and insert the name manually then s before I get all the posts.