I have set the member-profiles to be only visible by "Registered Members".
So there are 2 different behaviours when clicking on user-profiles at this page:
1) when clicking on a member-profile (avatar) in the members-list, then it does not open the Member-Card, but forwards directly to the Error-page which says "Login required".
2) when clicking on a member-profile (avatar) at the box in the Sidebar named "Highest-Posting Members", then it does indeed open the Member-Card. When clicking onto the Member-Card then it forwards to the Error-page which says "Login required".
So in one case the Member-Card is being opened up, in the other case the Member-Card does not open up.
Why the difference ?
Personaly I would prefer the Member-Card opening up and then forwarding to the Error-page.